Dual Core Golf Ball Having A Shallow &#34;Positive Hardness Gradient&#34; Thermoplastic Inner Core And A Steep &#34;Positive Hardness Gradient&#34; Thermoset Outer Core Layer

ABSTRACT

A golf ball includes an inner core layer including a thermoplastic highly-neutralized ionomer formed from a copolymer of ethylene and an α,β-unsaturated carboxylic acid, an organic acid or salt thereof, and sufficient cation source to neutralize the acid groups of the copolymer by 80% or greater. The inner core has a geometric center hardness and a surface hardness to define a first hardness gradient. An outer core layer is disposed about the inner core and is formed from a homogenous thermoset composition. The outer core layer has an interior hardness and an outer surface hardness to define a second hardness gradient. An inner cover layer is disposed about outer core layer and an outer cover layer is disposed about the inner cover layer. A slope of the second hardness gradient is greater than a slope of the first hardness gradient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 13/220,925, filed Aug. 30, 2011, which is acontinuation-in-part of co-pending U.S. patent application Ser. No.13/041,286, filed Mar. 4, 2011, which is a continuation of U.S. patentapplication Ser. No. 12/891,324, filed Sep. 27, 2010 and now U.S. Pat.No. 8,007,376, which is a continuation-in-part of U.S. patentapplication Ser. No. 12/339,495, filed Dec. 19, 2008 and now U.S. Pat.No. 7,815,526, which is a continuation-in-part of U.S. patentapplication Ser. No. 12/196,522, filed Aug. 22, 2008 and now U.S. Pat.No. 7,582,025, which is a continuation of U.S. patent application Ser.No. 11/939,635, filed Nov. 14, 2007 and now U.S. Pat. No. 7,427,242, thedisclosures of which are incorporated herein by reference thereto.

FIELD OF THE INVENTION

This invention relates generally to golf balls with cores and, moreparticularly cores having a thermoplastic inner core layer and athermoset outer core layer. Both the inner and outer core layers have a“positive hardness gradient,” the gradient of the outer core layer being‘steep’ and the gradient of the inner core being ‘shallow’.

BACKGROUND OF THE INVENTION

Solid golf balls are typically made with a solid core encased by acover, both of which can have multiple layers, such as a dual corehaving a solid center (or inner core) and an outer core layer, or amulti-layer cover having inner and outer cover layers. Generally, golfball cores and/or centers are constructed with a thermoset rubber, suchas a polybutadiene-based composition.

Thermoset polymers, once formed, cannot be reprocessed because themolecular chains are covalently bonded to one another to form athree-dimensional (non-linear) crosslinked network. The physicalproperties of the uncrosslinked polymer (pre-cure) are dramaticallydifferent than the physical properties of the crosslinked polymer(post-cure). For the polymer chains to move, covalent bonds would needto be broken—this is only achieved via degradation of the polymerresulting in dramatic loss of physical properties.

Thermoset rubbers are heated and crosslinked in a variety of processingsteps to create a golf ball core having certain desirablecharacteristics, such as higher or lower compression or hardness, thatcan impact the spin rate of the ball and/or provide better “feel.” Theseand other characteristics can be tailored to the needs of golfers ofdifferent abilities. Due to the nature of thermoset materials and theheating/curing cycles used to form them into cores, manufacturers canachieve varying properties across the core (i.e., from the core surfaceto the center of the core). For example, most conventional single coregolf ball cores have a ‘hard-to-soft’ hardness gradient from the surfaceof the core towards the center of the core.

In a conventional, polybutadiene-based core, the physical properties ofthe molded core are highly dependent on the curing cycle (i.e., the timeand temperature that the core is subjected to during molding). Thistime/temperature history, in turn, is inherently variable throughout thecore, with the center of the core being exposed to a differenttime/temperature (i.e., shorter time at a different temperature) thanthe surface (because of the time it takes to get heat to the center ofthe core) allowing a property gradient to exist at points between thecenter and core surface. This physical property gradient is readilymeasured as a hardness gradient, with a typical range of 5 to 40 ShoreC, and more commonly 10 to 30 Shore C, being present in virtually allgolf ball cores made from about the year 1970 on.

The patent literature contains a number of references that discuss‘hard-to-soft’ hardness gradients across a thermoset golf ball core.Additionally, a number of patents disclose multilayer thermoset golfball cores, where each core layer has a different hardness in an attemptto artificially create a hardness ‘gradient’ between core layer and corelayer. Because of the melt properties of thermoplastic materials,however, the ability to achieve varied properties across a golf ballcore has not been possible.

Unlike thermoset materials, thermoplastic polymers can be heated andre-formed, repeatedly, with little or no change in physical properties.For example, when at least the crystalline portion of a high molecularweight polymer is softened and/or melted (allowing for flow andformability), then cooled, the initial (pre-melting) and final(post-melting) molecular weights are essentially the same. The structureof thermoplastic polymers are generally linear, or slightly branched,and there is no intermolecular crosslinking or covalent bonding, therebylending these polymers their thermolabile characteristics. Therefore,with a thermoplastic core, the physical properties pre-molding areeffectively the same as the physical properties post-molding.Time/temperature variations have essentially no effect on the physicalproperties of a thermoplastic polymer.

As such, there is a need for a golf ball core, in particular a dualcore, that has a gradient from the surface to the center (or innerportion) of each core layer. The hardness gradient may be eithersoft-to-hard (a “negative hardness gradient”), hard-to-soft (a “positivehardness gradient”), measuring radially inward, or, in the case of adual core having a thermoplastic inner core layer, any combination ofhardness gradients for each core layer (e.g. positive/positive,positive/negative, negative/positive, or negative/negative). A coreexhibiting these various hardness gradients will allow the golf balldesigner to create a thermoplastic core golf ball with unique gradientproperties allowing for differences in ball characteristics such ascompression, “feel,” and spin.

SUMMARY OF THE INVENTION

The present invention is directed to a golf ball including an inner corelayer consisting essentially of a thermoplastic material and having ageometric center hardness greater than a surface hardness to define anegative hardness gradient; an outer core layer disposed about the innercore, the outer core being formed from a substantially homogenousthermoset composition and having an inner surface hardness substantiallyless than an outer surface hardness to define a positive hardnessgradient; an inner cover layer disposed outer core layer; and an outercover layer disposed about the inner cover layer, wherein the negativehardness gradient is from −1 to −5 Shore C, the positive hardnessgradient is 25 Shore C to 45 Shore C, and a difference between the innercore surface hardness and the outer core inner surface hardness, Δh, isat least 25 Shore C.

In one embodiment, the thermoplastic material includes an ionomer, ahighly-neutralized ionomer, a thermoplastic polyurethane, athermoplastic polyurea, a styrene block copolymer, a polyester amide,polyester ether, a polyethylene acrylic acid copolymer or terpolymer, ora polyethylene methacrylic acid copolymer or terpolymer.

Preferably, the difference between the inner core surface hardness andthe outer core inner surface hardness, Δh, is 25 Shore C to 45 Shore C,more preferably 30 Shore C to 35 Shore C. The inner core center hardnessshould be about 90 Shore C to about 100 Shore C. The inner core surfacehardness should be about 85 Shore C to about 95 Shore C. The hardness ofthe inner surface of the outer core layer should be about 50 Shore C toabout 60 Shore C. The hardness of the outer surface of the outer corelayer should be about 82 Shore C to about 92 Shore C.

Preferably, the outer core layer includes diene rubber and a metal saltof a carboxylic acid in an amount of about 25 phr to about 40 phr. Inanother preferred embodiment, the outer core layer comprises agradient-promoting additive, such as benzoquinones, resorcinols,catechols, quinhydrones, and hydroquinones. In one particularembodiment, hardness of the inner surface of the outer core layer andthe hardness of the outer surface of the outer core layer are both lessthan the hardness of the outer surface of the inner core. Optionally,the outer core layer includes a soft and fast agent.

The present invention is also directed to a golf ball including an innercore layer consisting of a thermoplastic material and having a geometriccenter hardness greater than a surface hardness to define a negativehardness gradient between −1 Shore C and −5 Shore C; an outer core layerdisposed about the inner core, the outer core being formed from asubstantially homogenous thermoset composition comprising a diene rubberand having an inner surface hardness less than an outer surface hardnessto define a substantially positive hardness gradient of at least 25Shore C; a cover layer disposed outer core layer, the cover layercomprising an inner cover layer comprising an ionomer and an outer coverlayer comprising a castable polyurethane or polyurea material, wherein adifference between the inner core surface hardness and the outer coreinner surface hardness, Δh, is 25 Shore C to 45 Shore C.

The present invention is further directed to a golf ball including aninner core layer consisting of a thermoplastic material and having ageometric center hardness greater than a surface hardness to define anegative hardness gradient between −1 Shore C and −5 Shore C, the centerhardness being about 90 Shore C to about 100 Shore C and the surfacehardness being about 85 Shore C to about 95 Shore C; an outer core layerdisposed about the inner core, the outer core being formed from asubstantially homogenous thermoset composition comprising a diene rubberand having an inner surface hardness less than an outer surface hardnessto define a positive hardness gradient of at least 25 Shore C, the innersurface being about 50 Shore C to about 60 Shore C and the surface beingabout 82 Shore C to about 92 Shore C; a cover layer disposed outer corelayer, the cover layer comprising an inner cover layer comprising anionomer and an outer cover layer comprising a castable polyurethane orpolyurea material, wherein a difference between the inner core surfacehardness and the outer core inner surface hardness, Δh, is 25 Shore C to40 Shore C.

The present invention is directed to a golf ball including a highlyneutralized thermoplastic inner core layer comprising ahighly-neutralized ionomer including a copolymer of ethylene and anα,β-unsaturated carboxylic acid, an organic acid or salt thereof, andsufficient cation source to neutralize the acid groups of the copolymerby 80% or greater. The inner core has a geometric center hardness lessthan its surface hardness to define a first hardness gradient. An outercore layer is disposed over the inner core and is formed from athermoset composition. The outer core layer has an interior hardnesssubstantially less than the hardness at its outer surface hardness todefine a second hardness gradient. An inner cover layer and an outercover layer are disposed about the core. The first and second hardnessgradients are positive and a slope of the second hardness gradient isgreater than a slope of the first hardness gradient.

In a preferred embodiment, a ratio of the slope of the second hardnessgradient to the slope of the first hardness gradient is greater than 1,more preferably greater than 1.5, most preferably greater than 2. Theinner core layer has an outer diameter of about 0.5 inches to about 1.13inches, preferably about 1 inch. In one embodiment, the first hardnessgradient is less than 10 Shore C and the second hardness gradient isgreater than 10 Shore C to define a steep positive hardness gradientouter core layer and a shallow positive hardness gradient inner core. Ina preferred embodiment, the first hardness gradient is less than 5 ShoreC and the second hardness gradient is greater than 15 Shore C.

The acid groups of the copolymer are neutralized by 90% or greater,preferably by about 100%. The organic acid or salt thereof typicallyincludes barium, lithium, sodium, zinc, bismuth, chromium, cobalt,copper, potassium, strontium, titanium, tungsten, magnesium, cesium,iron, nickel, silver, aluminum, tin, or calcium salts, or salts of fattyacids. In a preferred embodiment, the fatty acid salt includes stearicacid, behenic acid, erucic acid, oleic acid, linoelic acid or dimerizedderivatives thereof. Preferably, the organic acid or salt thereofincludes a magnesium salt of oleic acid. In another preferredembodiment, the outer core layer includes a soft and fast agent, morepreferably a halogenated thiophenol.

The present invention is further directed to a golf ball including aninner core layer consisting of a thermoplastic material and having ageometric center hardness less than a surface hardness to define a firstpositive hardness gradient of less than 10 Shore D points; an outer corelayer disposed about the inner core, the outer core being formed from asubstantially homogenous thermoset composition comprising a diene rubberand having a second positive hardness gradient of 10 Shore D points orgreater; a cover layer disposed outer core layer, the cover layercomprising an inner cover layer comprising an ionomer, and an outercover layer comprising a castable polyurethane or polyurea material.Preferably, a ratio of the second positive hardness gradient is greaterthan the first positive hardness gradient. In one preferred embodiment,the ratio is greater than 1.5, more preferably greater than 2.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing preferred hardness values and relationshipsbetween the “negative” hardness gradient thermoplastic inner core layerand the steep “positive” hardness gradient thermoset outer core layer ofthe present invention;

FIG. 2 depicts representative hardness measurements (in Shore C and D)and hardness gradient for a dual core having an inner core with adiameter of 0.5 inches and an outer core layer with a thickness of 0.515inches;

FIG. 3 depicts representative hardness measurements (in Shore C and D)and hardness gradient for a dual core having an inner core with adiameter of 1.0 inch and an outer core layer with a thickness of 0.275inches; and

FIG. 4 depicts representative hardness measurements (in Shore C and D)and hardness gradient for a dual core having an inner core with adiameter of 1.13 inches and an outer core layer with a thickness of0.225 inches.

DETAILED DESCRIPTION OF THE INVENTION

The golf balls of the present invention may include a single-layer(one-piece) golf ball, and multi-layer golf balls, such as one having acore and a cover surrounding the core, but are preferably formed from acore comprised of a solid center (otherwise known as an inner corelayer) and an outer core layer, and a cover layer. Of course, any of thecore and/or the cover layers may include more than one layer. In apreferred embodiment, the core is formed of a thermoplastic inner corelayer and a thermosetting rubber outer core layer where the inner corehas a “positive hardness gradient” as measured radially inward from theouter surface and the outer core layer also has a “hard-to-soft”hardness gradient (a “positive hardness gradient”) as measured radiallyinward from the outer core outer surface.

The inventive cores may have a hardness gradient defined by hardnessmeasurements made at the surface of the inner core (or outer core layer)and at points radially inward towards the center of the inner core,typically at 2-mm increments. As used herein, the terms “negativehardness gradient” and “positive hardness gradient” refer to the resultof subtracting the hardness value at the innermost portion of thecomponent being measured (e.g., the center of a solid core or an innercore in a dual core construction; the inner surface of a core layer;etc.) from the hardness value at the outer surface of the componentbeing measured (e.g., the outer surface of a solid core; the outersurface of an inner core in a dual core; the outer surface of an outercore layer in a dual core, etc.). For example, if the outer surface of asolid core has a lower hardness value than the center (i.e., the surfaceis softer than the center), the hardness gradient will be deemed a“negative” gradient (a smaller number−a larger number=a negativenumber).

In a preferred embodiment, the golf balls of the present inventioninclude an inner core layer formed from a thermoplastic (TP) material todefine a “positive hardness gradient” and an outer core layer formedfrom a thermoset (TS) material to define a steep “positive hardnessgradient.” The TP hardness gradient may be created by exposing the innercore layers to 1) a high-energy radiation treatment, such as electronbeam or gamma radiation, such as disclosed in U.S. Pat. No. 5,891,973,which is incorporated by reference thereto, 2) lower energy radiation,such as UV or IR radiation; 3) a solution treatment, such as anisocyanate or a silane; 4) incorporation of additional free radicalinitiator groups in the TP prior to molding; and/or 5) chemicalmodification, such as esterification or saponification, to name a few.

The magnitude of the “positive hardness gradient” of the inner corelayer is preferably “shallow” relative to the “steep” “positive hardnessgradient” of the outer core layer, the terms “shallow” and “steep” beingdefined by the slopes of their comparative plots of hardness as afunction of position away from the center of the core when the hardnessis measured across the cross-section of a core. For example, magnitudeof hardness change across either core layer may be similar or different,but in the case of similar hardness gradients, the gradient for theinner core may still be deemed “shallow” because the gradient ismeasured across a longer dimension than that of the outer core layer(i.e., a gradient of 10 Shore C across a 15-mm-radius inner core has amuch more gradual slope than a 10 Shore C gradient across a 5-mm-thickouter core layer). In a more preferred embodiment, the hardness gradientof the outer core layer is greater than or equal to the hardnessgradient of the inner core layer, most preferably the hardness gradientof the outer core layer is greater than the hardness gradient of theinner core layer.

Preferably, the core or core layers (inner core or outer core layer),most preferably the inner core layer, are formed from a compositionincluding at least one thermoplastic material. Preferably, thethermoplastic material comprises highly neutralized polymers;ethylene/acid copolymers and ionomers; ethylene/(meth)acrylateester/acid copolymers and ionomers; ethylene/vinyl acetates;polyetheresters; polyetheramides; thermoplastic polyurethanes;metallocene catalyzed polyolefins; polyalkyl(meth)acrylates;polycarbonates; polyamides; polyamide-imides; polyacetals; polyethylenes(i.e., LDPE, HDPE, UHMWPE); high impact polystyrenes;acrylonitrile-butadiene-styrene copolymers; polyesters; polypropylenes;polyvinyl chlorides; polyetheretherketones; polyetherimides;polyethersulfones; polyimides; polymethylpentenes; polystyrenes;polysulfones; or mixtures thereof. In a more preferred embodiment, thethermoplastic material is a highly-neutralized polymer, preferably afully-neutralized ionomer. Other suitable thermoplastic materials aredisclosed in U.S. Pat. Nos. 6,213,895 and 7,147,578, which areincorporated herein by reference thereto.

In a preferred embodiment, the inner core layer is formed from an HNPmaterial or a blend of HNP materials. The acid moieties of the HNP's,typically ethylene-based ionomers, are preferably neutralized greaterthan about 70%, more preferably greater than about 90%, and mostpreferably at least about 100%. The HNP's can be also be blended with asecond polymer component, which, if containing an acid group, may beneutralized in a conventional manner, by the organic fatty acids of thepresent invention, or both. The second polymer component, which may bepartially- or fully-neutralized, preferably comprises ionomericcopolymers and terpolymers, ionomer precursors, thermoplastics,polyamides, polycarbonates, polyesters, polyurethanes, polyureas,thermoplastic elastomers, polybutadiene rubber, balata,metallocene-catalyzed polymers (grafted and non-grafted), single-sitepolymers, high-crystalline acid polymers, cationic ionomers, and thelike. HNP polymers typically have a material hardness of between about20 and about 80 Shore D, and a flexural modulus of between about 3,000psi and about 200,000 psi.

In one embodiment of the present invention the HNP's are ionomers and/ortheir acid precursors that are preferably neutralized, either fully- orpartially-, with organic acid copolymers or the salts thereof. The acidcopolymers are preferably α-olefin, such as ethylene, C₃₋₈α,β-ethylenically unsaturated carboxylic acid, such as acrylic andmethacrylic acid, copolymers. They may optionally contain a softeningmonomer, such as alkyl acrylate and alkyl methacrylate, wherein thealkyl groups have from 1 to 8 carbon atoms.

The acid copolymers can be described as E/X/Y copolymers where E isethylene, X is an α,β-ethylenically unsaturated carboxylic acid, and Yis a softening comonomer. In a preferred embodiment, X is acrylic ormethacrylic acid and Y is a C₁₋₈ alkyl acrylate or methacrylate ester. Xis preferably present in an amount from about 1 to about 35 weightpercent of the polymer, more preferably from about 5 to about 30 weightpercent of the polymer, and most preferably from about 10 to about 20weight percent of the polymer. Y is preferably present in an amount fromabout 0 to about 50 weight percent of the polymer, more preferably fromabout 5 to about 25 weight percent of the polymer, and most preferablyfrom about 10 to about 20 weight percent of the polymer.

Specific acid-containing ethylene copolymers include, but are notlimited to, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylicacid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate,ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylicacid/n-butyl methacrylate, ethylene/acrylic acid/methyl methacrylate,ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/methacrylic acid/methyl methacrylate, andethylene/acrylic acid/n-butyl methacrylate. Preferred acid-containingethylene copolymers include, ethylene/methacrylic acid/n-butyl acrylate,ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/acrylic acid/ethyl acrylate, ethylene/methacrylicacid/ethyl acrylate, and ethylene/acrylic acid/methyl acrylatecopolymers. The most preferred acid-containing ethylene copolymers are,ethylene/(meth) acrylic acid/n-butyl, acrylate, ethylene/(meth)acrylicacid/ethyl acrylate, and ethylene/(meth) acrylic acid/methyl acrylatecopolymers.

Ionomers are typically neutralized with a metal cation, such as Li, Na,Mg, K, Ca, or Zn. It has been found that by adding sufficient organicacid or salt of organic acid, along with a suitable base, to the acidcopolymer or ionomer, however, the ionomer can be neutralized, withoutlosing processability, to a level much greater than for a metal cation,hence the term HNP. Preferably, the acid moieties are neutralizedgreater than about 80%, preferably from 90-100%, most preferably 100%without losing processability. This is accomplished by melt-blending anethylene α,β-ethylenically unsaturated carboxylic acid copolymer, forexample, with an organic acid or a salt of organic acid, and adding asufficient amount of a cation source to increase the level ofneutralization of all the acid moieties (including those in the acidcopolymer and in the organic acid) to greater than 90%, (preferablygreater than 100%).

The organic acids of the present invention are aliphatic, mono- ormulti-functional (saturated, unsaturated, or multi-unsaturated) organicacids. Salts of these organic acids may also be employed. The salts oforganic acids of the present invention include the salts of barium,lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium,strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver,aluminum, tin, or calcium, salts of fatty acids, particularly stearic,behenic, erucic, oleic, linoelic or dimerized derivatives thereof. It ispreferred that the organic acids and salts of the present invention berelatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending).

Set forth below are particularly suitable highly-neutralized polymercompositions for forming thermoplastic core layers. The followingcommercially-available materials were used in the below examples:

A-C® 5120 ethylene acrylic acid copolymer with an acrylic acid contentof 15%, A-C® 5180 ethylene acrylic acid copolymer with an acrylic acidcontent of 20%, A-C® 395 high density oxidized polyethylene homopolymer,and A-C® 575 ethylene maleic anhydride copolymer, commercially availablefrom Honeywell;

CB23 high-cis neodymium-catalyzed polybutadiene rubber, commerciallyavailable from Lanxess Corporation;

CA1700 Soya fatty acid, CA1726 linoleic acid, and CA1725 conjugatedlinoleic acid, commercially available from Chemical Associates;

Century® 1107 highly purified isostearic acid mixture of branched andstraight-chain C18 fatty acid, commercially available from ArizonaChemical;

Clarix® 011370-01 ethylene acrylic acid copolymer with an acrylic acidcontent of 13% and Clarix® 011536-01 ethylene acrylic acid copolymerwith an acrylic acid content of 15%, commercially available from A.Schulman Inc.;

Elvaloy® AC 1224 ethylene-methyl acrylate copolymer with a methylacrylate content of 24 wt %, Elvaloy® AC 1335 ethylene-methyl acrylatecopolymer with a methyl acrylate content of 35 wt %, Elvaloy® AC 2116ethylene-ethyl acrylate copolymer with an ethyl acrylate content of 16wt %, Elvaloy® AC 3427 ethylene-butyl acrylate copolymer having a butylacrylate content of 27 wt %, and Elvaloy® AC 34035 ethylene-butylacrylate copolymer having a butyl acrylate content of 35 wt %,commercially available from E.I. Dupont de Nemours and Company;

Escor® AT-320 ethylene acid terpolymer, commercially available fromExxonMobil Chemical Company;

Exxelor® VA 1803 amorphous ethylene copolymer functionalized with maleicanhydride, commercially available from ExxonMobil Chemical Company;

Fusabond® N525 metallocene-catalyzed polyethylene, Fusabond® N416chemically modified ethylene elastomer, Fusabond® C190 anhydridemodified ethylene vinyl acetate copolymer, and Fusabond® P614functionalized polypropylene, commercially available from E.I. Dupont deNemours and Company;

Hytrel® 3078 very low modulus thermoplastic polyester elastomer,commercially available from E.I. Dupont de Nemours and Company;

Kraton® FG 1901 GT linear triblock copolymer based on styrene andethylene/butylene with a polystyrene content of 30% and Kraton® FG1924GTlinear triblock copolymer based on styrene and ethylene/butylene with apolystyrene content of 13%, commercially available from KratonPerformance Polymers Inc.;

Lotader® 4603, 4700 and 4720, random copolymers of ethylene, acrylicester and maleic anhydride, commercially available from ArkemaCorporation;

Nordel® IP 4770 high molecular weight semi-crystalline EPDM rubber,commercially available from The Dow Chemical Company;

Nucrel® 9-1, Nucrel® 599, Nucrel® 960, Nucrel® 0407, Nucrel® 0609,Nucrel® 1214, Nucrel® 2906, Nucrel® 2940, Nucrel® 30707, Nucrel® 31001,and Nucrel® AE acid copolymers, commercially available from E.I. Dupontde Nemours and Company;

Primacor® 3150, 3330, 59801, and 59901 acid copolymers, commerciallyavailable from The Dow Chemical Company;

Royaltuf® 498 maleic anhydride modified polyolefin based on an amorphousEPDM, commercially available from Chemtura Corporation;

Sylfat® FA2 tall oil fatty acid, commercially available from ArizonaChemical;

Vamac® G terpolymer of ethylene, methylacrylate and a cure site monomer,commercially available from E.I. Dupont de Nemours and Company; and

XUS 60758.08L ethylene acrylic acid copolymer with an acrylic acidcontent of 13.5%, commercially available from The Dow Chemical Company.

Various compositions were melt blended using components as given inTable 18 below. The compositions were neutralized by adding a cationsource in an amount sufficient to neutralize, theoretically, 110% of theacid groups present in components 1 and 3, except for example 72, inwhich the cation source was added in an amount sufficient to neutralize75% of the acid groups. Magnesium hydroxide was used as the cationsource, except for example 68, in which magnesium hydroxide and sodiumhydroxide were used in an equivalent ratio of 4:1. In addition tocomponents 1-3 and the cation source, example 71 contains ethyl oleateplasticizer.

The relative amounts of component 1 and component 2 used are indicatedin Table 18 below, and are reported in wt %, based on the combinedweight of components 1 and 2. The relative amounts of component 3 usedare indicated in Table 1 below, and are reported in wt %, based on thetotal weight of the composition.

TABLE 1 Ex. Component 1 wt % Component 2 wt % Component 3 wt % 1Primacor 5980I 78 Lotader 4603 22 magnesium oleate 41.6 2 Primacor 5980I84 Elvaloy AC 1335 16 magnesium oleate 41.6 3 Primacor 5980I 78 ElvaloyAC 3427 22 magnesium oleate 41.6 4 Primacor 5980I 78 Elvaloy AC 1335 22magnesium oleate 41.6 5 Primacor 5980I 78 Elvaloy AC 1224 22 magnesiumoleate 41.6 6 Primacor 5980I 78 Lotader 4720 22 magnesium oleate 41.6 7Primacor 5980I 85 Vamac G 15 magnesium oleate 41.6 8 Primacor 5980I 90Vamac G 10 magnesium oleate 41.6 8.1 Primacor 5990I 90 Fusabond 614 10magnesium oleate 41.6 9 Primacor 5980I 78 Vamac G 22 magnesium oleate41.6 10 Primacor 5980I 75 Lotader 4720 25 magnesium oleate 41.6 11Primacor 5980I 55 Elvaloy AC 3427 45 magnesium oleate 41.6 12 Primacor5980I 55 Elvaloy AC 1335 45 magnesium oleate 41.6 12.1 Primacor 5980I 55Elvaloy AC 34035 45 magnesium oleate 41.6 13 Primacor 5980I 55 ElvaloyAC 2116 45 magnesium oleate 41.6 14 Primacor 5980I 78 Elvaloy AC 3403522 magnesium oleate 41.6 14.1 Primacor 5990I 80 Elvaloy AC 34035 20magnesium oleate 41.6 15 Primacor 5980I 34 Elvaloy AC 34035 66 magnesiumoleate 41.6 16 Primacor 5980I 58 Vamac G 42 magnesium oleate 41.6 17Primacor 5990I 80 Fusabond 416 20 magnesium oleate 41.6 18 Primacor5980I 100 — — magnesium oleate 41.6 19 Primacor 5980I 78 Fusabond 416 22magnesium oleate 41.6 20 Primacor 5990I 100 — — magnesium oleate 41.6 21Primacor 5990I 20 Fusabond 416 80 magnesium oleate 41.6 21.1 Primacor5990I 20 Fusabond 416 80 magnesium oleate 31.2 21.2 Primacor 5990I 20Fusabond 416 80 magnesium oleate 20.8 22 Clarix 011370 30.7 Fusabond 41669.3 magnesium oleate 41.6 23 Primacor 5990I 20 Royaltuf 498 80magnesium oleate 41.6 24 Primacor 5990I 80 Royaltuf 498 20 magnesiumoleate 41.6 25 Primacor 5990I 80 Kraton FG1924GT 20 magnesium oleate41.6 26 Primacor 5990I 20 Kraton FG1924GT 80 magnesium oleate 41.6 27Nucrel 30707 57 Fusabond 416 43 magnesium oleate 41.6 28 Primacor 5990I80 Hytrel 3078 20 magnesium oleate 41.6 29 Primacor 5990I 20 Hytrel 307880 magnesium oleate 41.6 30 Primacor 5980I 26.8 Elvaloy AC 34035 73.2magnesium oleate 41.6 31 Primacor 5980I 26.8 Lotader 4603 73.2 magnesiumoleate 41.6 32 Primacor 5980I 26.8 Elvaloy AC 2116 73.2 magnesium oleate41.6 33 Escor AT-320 30 Elvaloy AC 34035 52 magnesium oleate 41.6Primacor 5980I 18 34 Nucrel 30707 78.5 Elvaloy AC 34035 21.5 magnesiumoleate 41.6 35 Nucrel 30707 78.5 Fusabond 416 21.5 magnesium oleate 41.636 Primacor 5980I 26.8 Fusabond 416 73.2 magnesium oleate 41.6 37Primacor 5980I 19.5 Fusabond N525 80.5 magnesium oleate 41.6 38 Clarix011536-01 26.5 Fusabond N525 73.5 magnesium oleate 41.6 39 Clarix011370-01 31 Fusabond N525 69 magnesium oleate 41.6 39.1 XUS 60758.08L29.5 Fusabond N525 70.5 magnesium oleate 41.6 40 Nucrel 31001 42.5Fusabond N525 57.5 magnesium oleate 41.6 41 Nucrel 30707 57.5 FusabondN525 42.5 magnesium oleate 41.6 42 Escor AT-320 66.5 Fusabond N525 33.5magnesium oleate 41.6 43 Nucrel 2906/2940 21 Fusabond N525 79 magnesiumoleate 41.6 44 Nucrel 960 26.5 Fusabond N525 73.5 magnesium oleate 41.645 Nucrel 1214 33 Fusabond N525 67 magnesium oleate 41.6 46 Nucrel 59940 Fusabond N525 60 magnesium oleate 41.6 47 Nucrel 9-1 44.5 FusabondN525 55.5 magnesium oleate 41.6 48 Nucrel 0609 67 Fusabond N525 33magnesium oleate 41.6 49 Nucrel 0407 100 — — magnesium oleate 41.6 50Primacor 5980I 90 Fusabond N525 10 magnesium oleate 41.6 51 Primacor5980I 80 Fusabond N525 20 magnesium oleate 41.6 52 Primacor 5980I 70Fusabond N525 30 magnesium oleate 41.6 53 Primacor 5980I 60 FusabondN525 40 magnesium oleate 41.6 54 Primacor 5980I 50 Fusabond N525 50magnesium oleate 41.6 55 Primacor 5980I 40 Fusabond N525 60 magnesiumoleate 41.6 56 Primacor 5980I 30 Fusabond N525 70 magnesium oleate 41.657 Primacor 5980I 20 Fusabond N525 80 magnesium oleate 41.6 58 Primacor5980I 10 Fusabond N525 90 magnesium oleate 41.6 59 — — Fusabond N525 100magnesium oleate 41.6 60 Nucrel 0609 40 Fusabond N525 20 magnesiumoleate 41.6 Nucrel 0407 40 61 Nucrel AE 100 — — magnesium oleate 41.6 62Primacor 5980I 30 Fusabond N525 70 CA1700 soya fatty acid 41.6 magnesiumsalt 63 Primacor 5980I 30 Fusabond N525 70 CA1726 linoleic acid 41.6magnesium salt 64 Primacor 5980I 30 Fusabond N525 70 CA1725 41.6conjugated linoleic acid magnesium salt 65 Primacor 5980I 30 FusabondN525 70 Century 1107 41.6 isostearic acid magnesium salt 66 A-C 512073.3 Lotader 4700 26.7 magnesium oleate 41.6 67 A-C 5120 73.3 Elvaloy34035 26.7 magnesium oleate 41.6 68 Primacor 5980I 78.3 Lotader 470021.7 magnesium oleate and 41.6 sodium salt 69 Primacor 5980I 47 ElvaloyAC34035 13 — — A-C 5180 40 70 Primacor 5980I 30 Fusabond N525 70 SylfatFA2 41.6 magnesium salt 71 Primacor 5980I 30 Fusabond N525 70 magnesiumoleate 31.2 ethyl oleate 10   72 Primacor 5980I 80 Fusabond N525 20sebacic acid 41.6 magnesium salt 73 Primacor 5980I 60 — — — — A-C 518040 74 Primacor 5980I 78.3 — — magnesium oleate 41.6 A-C 575 21.7 75Primacor 5980I 78.3 Exxelor VA 1803 21.7 magnesium oleate 41.6 76Primacor 5980I 78.3 A-C 395 21.7 magnesium oleate 41.6 77 Primacor 5980I78.3 Fusabond C190 21.7 magnesium oleate 41.6 78 Primacor 5980I 30Kraton FG 1901 70 magnesium oleate 41.6 79 Primacor 5980I 30 Royaltuf498 70 magnesium oleate 41.6 80 A-C 5120 40 Fusabond N525 60 magnesiumoleate 41.6 81 Primacor 5980I 30 Fusabond N525 70 erucic acid 41.6magnesium salt 82 Primacor 5980I 30 CB23 70 magnesium oleate 41.6 83Primacor 5980I 30 Nordel IP 4770 70 magnesium oleate 41.6 84 Primacor5980I 48 Fusabond N525 20 magnesium oleate 41.6 A-C 5180 32 85 Nucrel2806 22.2 Fusabond N525 77.8 magnesium oleate 41.6 86 Primacor 3330 61.5Fusabond N525 38.5 magnesium oleate 41.6 87 Primacor 3330 45.5 FusabondN525 20 magnesium oleate 41.6 Primacor 3150 34.5 88 Primacor 3330 28.5 —— magnesium oleate 41.6 Primacor 3150 71.5 89 Primacor 3150 67 FusabondN525 33 magnesium oleate 41.6 90 Primacor 5980I 55 Elvaloy AC 34035 45magnesium oleate lt 31.2 ethyl oleate 10  

Solid spheres of each composition were injection molded, and the solidsphere COR, compression, Shore D hardness, and Shore C hardness of theresulting spheres were measured after two weeks. The results arereported in Table 2 below.

TABLE 2 Solid Sphere Solid Sphere Solid Sphere Solid Sphere Ex. CORCompression Shore D Shore C 1 0.845 120 59.6 89.2 3 0.871 117 57.7 88.64 0.867 122 63.7 90.6 5 0.866 119 62.8 89.9 8.1 0.869 127 65.3 92.9 120.856 101 55.7 82.4 12.1 0.857 105 53.2 81.3 14 0.873 122 64.0 91.1 170.878 117 60.1 89.4 18 0.853 135 67.6 94.9 20 0.857 131 66.2 94.4 210.752 26 34.8 57.1 21.1 0.729 9 34.3 56.3 21.2 0.720 2 33.8 55.2 30 **66 42.7 65.5 31 0.730 67 45.6 68.8 32 ** 100 52.4 78.2 33 0.760 64 43.664.5 34 0.814 91 52.8 80.4 51 0.873 121 61.5 90.2 52 0.870 116 60.4 88.253 0.865 107 57.7 84.4 54 0.853 97 53.9 80.2 55 0.837 82 50.1 75.5 560.818 66 45.6 70.7 57 0.787 45 41.3 64.7 58 0.768 26 35.9 57.3 ** spherebroke during measurement

The ionomers of the invention may also include more conventionalionomers, i.e., partially-neutralized with metal cations. The acidmoiety in the acid copolymer is neutralized about 1 to about 90%,preferably at least about 20 to about 75%, and more preferably at leastabout 40 to about 70%, to form an ionomer, by a cation such as lithium,sodium, potassium, magnesium, calcium, barium, lead, tin, zinc,aluminum, or a mixture thereof.

The cores (and, preferably the inner core layer) may also be formed from(or contain as part of a blend) thermoplastic non-ionomer resins. Thesepolymers typically have a hardness in the range of 20 Shore D to 70Shore D. Examples of thermoplastic non-ionomers include, but are notlimited to, ethylene-ethyl acrylate, ethylene-methyl acrylate,ethylene-vinyl acetate, low density polyethylene, linear low densitypolyethylene, metallocene catalyzed polyolefins, polyamides includingnylon copolymers and nylon-ionomer graft copolymers, non-ionomeric acidcopolymers, and a variety of thermoplastic elastomers, includingstyrene-butadiene-styrene block copolymers, thermoplastic blockpolyamides, polyurethanes, polyureas, thermoplastic block polyesters,functionalized (e.g., maleic anhydride modified) EPR and EPDM, andsyndiotactic butadiene resin.

In order to obtain the desired Shore D hardness, it may be necessary toadd one or more crosslinking monomers and/or reinforcing agents to thepolymer composition. Nonlimiting examples of crosslinking monomers arezinc diacrylate, zinc dimethacrylate, ethylene dimethacrylate,trimethylol propane triacrylate. If crosslinking monomers are used, theytypically are added in an amount of 3 to 40 parts (by weight based upon100 parts by weight of polymer), and more preferably 5 to 30 parts.

Other layers of a dual core, preferably the outer core layer, may beformed from a rubber-based composition treated to define a steep“positive” hardness gradient, and preferably the inner core layer isformed from the thermoplastic material of the invention and has a“positive hardness gradient” that is ‘shallow’ relative to the gradientof the outer core layer. For example, the inner core may be formed fromthe ‘hardness gradient’ thermoplastic material of the invention to formthe shallow “positive hardness gradient” and the outer core layer mayinclude the thermosetting rubber composition having a ‘steep’ “positivehardness gradient.” The terms ‘steep’ and ‘shallow’ refer to themagnitude of the slope of the hardness gradients of the respectivelayers—as long as the slope of the hardness gradient of the outer corelayer is greater than that of the inner core layer, it will be termed‘steep’ (and the inner core layer deemed ‘shallow’).

A base thermoset rubber, which can be blended with other rubbers andpolymers, typically includes a natural or synthetic rubber. A preferredbase rubber is 1,4-polybutadiene having a cis structure of at least 40%,preferably greater than 80%, and more preferably greater than 90%. Othersuitable thermoset rubbers and preferred properties, such as Mooneyviscosity, are disclosed in U.S. Pat. No. 7,351,165, filed Mar. 13,2007, and U.S. Pat. No. 7,458,905, filed Mar. 23, 2007, both of whichare incorporated herein by reference.

Other thermoplastic elastomers may be used to modify the properties ofthe thermoplastic materials of the invention by blending with the basethermoplastic material. These TPEs include natural or synthetic balata,or high trans-polyisoprene, high trans-polybutadiene, or any styrenicblock copolymer, such as styrene ethylene butadiene styrene,styrene-isoprene-styrene, etc., a metallocene or other single-sitecatalyzed polyolefin such as ethylene-octene, or ethylene-butene, orthermoplastic polyurethanes (TPU), including copolymers, e.g. withsilicone. Other suitable TPEs include PEBAX®, which is believed tocomprise polyether amide copolymers, HYTREL®, which is believed tocomprise polyether ester copolymers, thermoplastic urethane, andKRATON®, which is believed to comprise styrenic block copolymerselastomers. Any of the TPEs or TPUs above may also contain functionalitysuitable for grafting, including maleic acid or maleic anhydride.

Additional polymers may also optionally be incorporated into theinventive cores (and layers thereof). Examples include, but are notlimited to, thermoset elastomers such as core regrind, thermoplasticvulcanizate, copolymeric ionomer, terpolymeric ionomer, polycarbonate,polyamide, copolymeric polyamide, polyesters, polyvinyl alcohols,acrylonitrile-butadiene-styrene copolymers, polyarylate, polyacrylate,polyphenylene ether, impact-modified polyphenylene ether, high impactpolystyrene, diallyl phthalate polymer, styrene-acrylonitrile polymer(SAN) (including olefin-modified SAN andacrylonitrile-styrene-acrylonitrile polymer), styrene-maleic anhydridecopolymer, styrenic copolymer, functionalized styrenic copolymer,functionalized styrenic terpolymer, styrenic terpolymer, cellulosepolymer, liquid crystal polymer, ethylene-vinyl acetate copolymers,polyurea, and polysiloxane or any metallocene-catalyzed polymers ofthese species.

Suitable polyamides for use as an additional polymeric material incompositions within the scope of the present invention also includeresins obtained by: (1) polycondensation of (a) a dicarboxylic acid,such as oxalic acid, adipic acid, sebacic acid, terephthalic acid,isophthalic acid, or 1,4-cyclohexanedicarboxylic acid, with (b) adiamine, such as ethylenediamine, tetramethylenediamine,pentamethylenediamine, hexamethylenediamine, or decamethylenediamine,1,4-cyclohexanediamine, or m-xylylenediamine; (2) a ring-openingpolymerization of cyclic lactam, such as ε-caprolactam or Ω-laurolactam;(3) polycondensation of an aminocarboxylic acid, such as 6-aminocaproicacid, 9-aminononanoic acid, 11-aminoundecanoic acid, or12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam witha dicarboxylic acid and a diamine. Specific examples of suitablepolyamides include NYLON 6, NYLON 66, NYLON 610, NYLON 11, NYLON 12,copolymerized NYLON, NYLON MXD6 (m-xylylene diamine/adipic acid), andNYLON 46.

Modifications in thermoplastic polymeric structure to create the‘shallow’ “positive hardness gradient” can be induced by a number ofmethods, including exposing the TP material to high-energy radiation orthrough a chemical process using peroxide. Radiative sources include,but are not limited to, gamma rays, electrons, neutrons, protons,x-rays, helium nuclei, or the like. Gamma radiation, typically usingradioactive cobalt atoms, is a preferred method for the inventive TPgradient cores because this type of radiation allows for considerabledepth of treatment, if necessary. For cores requiring lower depth ofpenetration, such as when a small gradient is desired or one focusednear the core surface, electron-beam accelerators or UV and IR lightsources can be used. Useful UV and IR irradiation methods are disclosedin U.S. Pat. Nos. 6,855,070 and 7,198,576, which are incorporated hereinby reference thereto. The cores of the invention are typicallyirradiated at dosages greater than 0.05 Mrd, preferably ranging from 1Mrd to 20 Mrd, more preferably from 2 Mrd to 15 Mrd, and most preferablyfrom 4 Mrd to 10 Mrd. In one preferred embodiment, the cores areirradiated at a dosage from 5 Mrd to 8 Mrd and in another preferredembodiment, the cores are irradiated with a dosage from 0.05 Mrd to 3Mrd, more preferably 0.05 Mrd to 1.5 Mrd.

While a number of methods known in the art are suitable for irradiatingthe TP (or TS) materials/cores, typically the cores are placed on andslowly move along a channel. Radiation from a radiation source, such asgamma rays, is allowed to contact the surface of the cores. The sourceis positioned to provide a generally uniform dose of radiation to thecores as they roll along the channel. The speed of the cores as theypass through the radiation source is easily controlled to ensure thecores receive sufficient dosage to create the desired hardness gradient.The cores are irradiated with a dosage of 1 or more Mrd, more preferably2 Mrd to 15 Mrd. The intensity of the dosage is typically in the rangeof 1 MeV to 20 MeV.

For thermoplastic resins having a reactive group (e.g., ionomer,thermoplastic urethane, etc.), treating the thermoplastic core in achemical solution of an isocyanate or and amine affects crosslinking andprovide a harder surface and subsequent hardness gradient. Incorporationof peroxide or other free-radical initiator in the thermoplasticpolymer, prior to molding or forming, also allows for heat curing on themolded core/core layer to create the desired gradient. By properselection of time/temperature, an annealing process can be used tocreate a gradient. Suitable annealing and/or peroxide (free radical)methods are such as disclosed in U.S. Pat. Nos. 5,274,041 and 5,356,941,respectively, which are incorporated by reference thereto. Additionally,silane or amino-silane crosslinking may also be employed as disclosed inU.S. Pat. No. 7,279,529, incorporated herein by reference.

The inventive cores (or core layers) may be chemically treated in asolution, such as a solution containing one or more isocyanates, to formthe desired “positive hardness gradient.” The cores are typicallyexposed to the solution containing the isocyanate by immersing them in abath at a particular temperature for a given time. Exposure time shouldbe greater than 1 minute, preferably from 1 minute to 120 minutes, morepreferably 5 minutes to 90 minutes, and most preferably 10 minutes to 60minutes. In one preferred embodiment, the cores are immersed in thetreating solution from 15 minutes to 45 minutes, more preferably from 20minutes to 40 minutes, and most preferably from 25 minutes to 30minutes.

Preferred isocyanates include aliphatic or aromatic isocyanates, such asHDI, IPDI, MDI, TDI, or diisocyanate or blends thereof known in the art.The isocyanate or diisocyanate used may have a solids content in therange of 1 wt % to 100 wt % solids, preferably 5 wt % to 50 wt % solids,most preferably 10 wt % to 30 wt % solids. In a most preferredembodiment, the cores of the invention are immersed in a solution of MDI(such as Mondur ML™, commercially available from Bayer) at 15 wt % to 30wt % solids in ketone for 20 minutes to 30 minutes. Suitable solvents(i.e., those that will allow penetration of the isocyanate into the TPmaterial) may be used. Preferred solvents include ketone and acetate.After immersion, the balls are typically air-dried and/or heated.Suitable isocyanates and treatment methods are disclosed in U.S. Pat.No. 7,118,496, which is incorporated herein by reference thereto.

Preferred silanes include, but are not limited to, compounds having theformula:

wherein R′ is a non-hydrolysable organofunctional group, X is ahydrolysable group, and n is 0-24. The non-hydrolysable organofunctionalgroup typically can link (either by forming a covalent or by anotherbinding mechanism, such as hydrogen bond) to a polymer, such as apolyolefin, thereby attaching the silane to the polymer. R′ ispreferably a vinyl group. X is preferably alkoxy, acyloxy, halogen,amino, hydrogen, ketoximate group, amido group, aminooxy, mercapto,alkenyloxy group, and the like. Preferably, X is an alkoxy, RO—, whereinR is selected from the group consisting of a linear or branched C₁-C₈alkyl group, a C₆-C₁₂ aromatic group, and R³C(O)—, wherein R³ is alinear or branched C₁-C₈ alkyl group. Typically, the silane can belinked to the polymer in one of two ways: by reaction of the silane tothe finished polymer or copolymerizing the silane with the polymerprecursors.

A preferred silane may also have the formula R′—(CH₂)_(n)SiX_(k)Q_(m) or[R′—(CH₂)_(n)]₂Si(X)_(p)Q_(q), wherein R′ is an unsaturated vinyl group;Q is selected from the group consisting of an isocyanate functionality,i.e., a monomer, a biuret, or an isocyanurate; a glycidyl, a halo groupand —NR¹R², wherein R¹ and R² are each independently selected from thegroup consisting of H, a linear or branched C₁-C₈ alkyl group, a linearor branched C₁-C₈ alkenyl group and a linear or branched C₁-C₈ alkynylgroup; X is a hydrolysable group; and n is 0-24, k is 1-3, m is 3-n, pis 1-2 and q is 2-p. X is preferably alkoxy, acyloxy, halogen, amino,hydrogen, ketoximate group, amido group, aminooxy, mercapto, alkenyloxygroup, and the like. Preferably, the halo group is fluoro, chloro, bromoor iodo and is preferably chloro.

The unsaturated group A is represented by the formula:

wherein R¹, R², and R³ are each independently selected from the groupconsisting of a substituted or unsubstituted linear or branched C₁-C₈alkyl group, a substituted or unsubstituted C₆-C₁₂ aromatic group and ahalo group. Preferred halo groups include F, Cl or Br. The C₁-C₈ alkylgroups and the C₆-C₁₂ aromatic groups may be substituted with one ormore C₁-C₆ alkyl groups, halo groups, such as F, Cl and Br, amines, CN,C₁-C₆ alkoxy groups, trihalomethane, such as CF₃ or CCl₃, or mixturesthereof. Preferably, R¹, R², and R³ are each independently selected fromthe group consisting of hydrogen, methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl and tert-butyl. More preferably, R¹, R², and R³ areeach independently hydrogen or methyl.

Thus in a preferred embodiment, the silane is a vinyltrialkoxysilane,such as vinyltrimethoxysilane, vinyldimethoxysilane,vinyltrimethoxysilane, vinylmethoxysilane, vinyltriethoxysilane,vinyldiphenylchlorosilane, vinyltrichlorosilane, vinylsilane,(vinyl)(methyl)diethoxysilane, vinyltriacetoxysilane,vinyltris(2-methoxyethoxy)silane, vinyl triphenylsilane, and(vinyl)(dimethyl)chlorosilane.

The silanes of the present invention are present from about 0.1 weightpercent to about 100 weight percent of the polyolefin. Typically, thesilanes are present from about 0.5 weight percent to about 50 weightpercent of the polyolefin, preferably from about 1 weight percent toabout 20 weight percent of the polyolefin, more preferably from about 2weight percent to about 10 weight percent of polyolefin and even morepreferably from about 3 weight percent to about 5 weight percent. Asused herein, all upper and lower limits of the ranges disclosed hereincan be interchanged to form new ranges. Thus, the present invention alsoencompasses silane amounts of from about 0.1 weight percent to about 5weight percent of polyolefin, from about 1 weight percent to about 10weight percent of polyolefin, and even from 20 weight percent to about50 weight percent.

Commercially available silanes for moisture crosslinking may be used toform golf ball components and golf balls. A nonlimiting example of asuitable silane is SILCAT® RHS Silane, a multi-component crosslinkingsystem for use in moisture crosslinking of stabilized polyethylene orethylene copolymers (available at Crompton Corporation, Middlebury,Conn.). IN addition, functionalized resin systems also may be used, suchas SYNCURE®, which is a silane-grafted, moisture-crosslinkablepolyethylene system available from PolyOne Corporation of Cleveland,Ohio, POLIDAN®, which is a silane-crosslinkable HDPE available fromSolvay of Padanaplast, Italy, and VISICO™/AMBICAT™, which is apolyethylene system that utilizes a non-tin catalyst in crosslinkingavailable from Borealis of Denmark.

Other suitable silanes include, but are not limited to, silane esters,such as octyltriethoxysilane, methyltriethoxylsilane,methyltrimethoxysilane, and proprietary nonionic silane dispersingagent; vinyl silanes, such as proprietary, vinyltriethoxysilane,vinyltrimethoxysilane, vinyl-tris-(2-methoxyethoxy) silane,vinylmethyldimethoxysilane; methacryloxy silanes, such asγ-methacryloxypropyltrimethoxysilane; epoxy silanes, such asβ-(3,4-epoxycyclohexyl) ethyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane; sulfur silanes, such asgamma-mercaptopropyltrimethoxysilane proprietary polysulfidesilane,bis-(3-[triethoxisily]-propyl)-tetrasulfane; amino silanes, such asγ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane,γ-aminopropyltriethoxysilane, aminoalkyl silicone solution, modifiedaminoorganosilane, gamma-aminopropyltrimethoxysilane,n-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, modifiedaminoorganosilane (40% in methanol), modified aminosilane (50% inmethanol), triaminofunctional silane,bis-(γ-trimethoxysilylpropyl)amine,n-phenyl-γ-aminopropyltrimethoxysilane, organomodifiedpolydimethylsiloxane, polyazamide silane (50% in methanol),n-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane; ureido silanes,such as gamma-ureidopropyltrialkoxysilane (50% in methanol),γ-ureidopropyltrimethoxysilane; isocyanate silanes, such asγ-isocyanatopropyltriethoxysilane; and mixtures thereof. Preferably, thesilane is an amino silane and more preferably, the amino silane isbis-(γ-trimethoxysilylpropyl) amine.

Both irradiative and chemical methods promote molecular bonding, orcross-links, within the TP polymer. Radiative methods permitcross-linking and grafting in situ on finished products andcross-linking occurs at lower temperatures with radiation than withchemical processing. Chemical methods depend on the particular polymer,the presence of modifying agents, and variables in processing, such asthe level of irradiation. Significant property benefits in the TP corescan be attained and include, but are not limited to, improvedthermomechanical properties; lower permeability and improved chemicalresistance; reduced stress cracking; and overall improvement in physicaltoughness.

Additional embodiments involve the use of plasticizers to treat themolded core/layer thereby creating a softer outer portion of the corefor a “negative” hardness gradient. The plasticizer may be reactive(such as higher alkyl acrylates) or non-reactive (i.e., phthalates,dioctylphthalate, or stearamides, etc). Other suitable plasticizersinclude, but are not limited to, oxa acids, fatty amines, fatty amides,fatty acid esters, phthalates, adipates, and sebacates. Oxa acids arepreferred plasticizers, more preferably those having at least one or twoacid functional groups and a variety of different chain lengths.Preferred oxa acids include 3,6-dioxaheptanoic acid,3,6,9-trioxadecanoic acid, diglycolic acid, 3,6,9-trioxaundecanoic acid,polyglycol diacid, and 3,6-dioxaoctanedioic acid, such as thosecommercially available from Archimica of Wilmington, Del. Any means ofchemical degradation will also result in a “negative” hardness gradient.

Chemical modifications such as esterification or saponification are alsosuitable for modification of the thermoplastic core/layer surface andcan result in the desired ‘shallow’ “positive hardness gradient.”Fillers may also be added to the thermoplastic materials of the core toadjust the density of the material up or down.

The ‘steep’ “negative” or, preferably, “positive hardness gradient”outer core layer(s) are formed from a composition including at least onebase rubber, such as a polybutadiene rubber, cured with at least oneperoxide and at least one reactive co-agent, which can be a metal saltof an unsaturated carboxylic acid, such as acrylic acid or methacrylicacid, a non-metallic coagent, or mixtures thereof. For the “negative”hardness gradient embodiments, a suitable antioxidant can be included inthe core layer composition. An optional ‘soft and fast agent’ (andsometimes a cis-to-trans catalyst), such as an organosulfur ormetal-containing organosulfur compound, can also be included in the corelayer formulation. To form the steep “positive hardness gradient” acrossthe outer core layers of the invention, a gradient-promoting additive(GPA) is preferably added to the outer core layer compositions. SuitableGPA's are discussed below.

Other ingredients that are known to those skilled in the art may beused, and are understood to include, but not be limited to,density-adjusting fillers, process aides, plasticizers, blowing orfoaming agents, sulfur accelerators, and/or non-peroxide radicalsources.

The base thermoset rubber, which can be blended with other rubbers andpolymers, typically includes a natural or synthetic rubber. A preferredbase rubber is 1,4-polybutadiene having a cis structure of at least 40%,preferably greater than 80%, and more preferably greater than 90%.

Examples of desirable polybutadiene rubbers include BUNA® CB 1203, CB1220, CB1221, CB22 and CB23, commercially available from LANXESSCorporation; UBEPOL® 360L and UBEPOL® 150L and UBEPOL-BR rubbers,commercially available from UBE Industries, Ltd. of Tokyo, Japan;Europrene® NEOCIS® BR 40 and BR 60, commercially available from PolimeriEuropa; and BR 01, BR 730, BR 735, BR 11, and BR 51, commerciallyavailable from Japan Synthetic Rubber Co., Ltd; BUNA® CB Nd40 fromLanxess; and KARBOCHEM® ND40, ND45, and ND60, commercially availablefrom Karbochem.

The base rubber may also comprise high or medium Mooney viscosityrubber, or blends thereof. The measurement of Mooney viscosity isdefined according to ASTM D-1646. The Mooney viscosity range ispreferably greater than about 40, more preferably in the range fromabout 40 to about 80 and more preferably in the range from about 40 toabout 60. Polybutadiene rubber with higher Mooney viscosity may also beused, so long as the viscosity of the polybutadiene does not reach alevel where the high viscosity polybutadiene clogs or otherwiseadversely interferes with the manufacturing machinery. It iscontemplated that polybutadiene with viscosity less than 65 Mooney canbe used with the present invention. In one embodiment of the presentinvention, golf ball core layers made with mid- to high-Mooney viscositypolybutadiene material exhibit increased resiliency (and, therefore,distance) without increasing the hardness of the ball.

Commercial sources of suitable mid- to high-Mooney viscositypolybutadiene include BUNA® CB23 (Nd-catalyzed), which has a Mooneyviscosity of around 50 and is a highly linear polybutadiene, and BUNA®CB 1220 (Co-catalyzed). If desired, the polybutadiene can also be mixedwith other elastomers known in the art, such as other polybutadienerubbers, natural rubber, styrene butadiene rubber, and/or isoprenerubber in order to further modify the properties of the core. When amixture of elastomers is used, the amounts of other constituents in thecore composition are typically based on 100 parts by weight of the totalelastomer mixture.

In one preferred embodiment, the base rubber comprises a Nd-catalyzedpolybutadiene, a transition metal polybutadiene rubber, or blendsthereof. If desired, the polybutadiene can also be mixed with otherelastomers known in the art such as natural rubber, polyisoprene rubberand/or styrene-butadiene rubber in order to modify the properties of thecore. Other suitable base rubbers include thermosetting materials suchas, ethylene propylene diene monomer rubber, ethylene propylene rubber,butyl rubber, halobutyl rubber, hydrogenated nitrile butadiene rubber,nitrile rubber, and silicone rubber.

Thermoplastic elastomers (TPE) many also be used to modify theproperties of the core layers, or the uncured core layer stock byblending with the base rubber. These TPEs include styrenic blockcopolymers, such as styrene ethylene butadiene styrene,styrene-isoprene-styrene, etc., a metallocene or other single-sitecatalyzed polyolefin such as ethylene-octene, or ethylene-butene, orthermoplastic polyurethanes (TPU), including copolymers, e.g. withsilicone. Other suitable TPEs for blending with the thermoset rubbers ofthe present invention include PEBAX®, which is believed to comprisepolyether amide copolymers, HYTREL®, which is believed to comprisepolyether ester copolymers, thermoplastic urethane, and KRATON®, whichis believed to comprise styrenic block copolymers elastomers. Any of theTPEs or TPUs above may also contain functionality suitable for grafting,including maleic acid or maleic anhydride.

Additional polymers may also optionally be incorporated into the baserubber. Examples include, but are not limited to, thermoset elastomerssuch as core regrind, thermoplastic vulcanizate, copolymeric ionomer,terpolymeric ionomer, polycarbonate, polyamide, copolymeric polyamide,polyesters, polyvinyl alcohols, acrylonitrile-butadiene-styrenecopolymers, polyarylate, polyacrylate, polyphenylene ether,impact-modified polyphenylene ether, high impact polystyrene, diallylphthalate polymer, styrene-acrylonitrile polymer (SAN) (includingolefin-modified SAN and acrylonitrile-styrene-acrylonitrile polymer),styrene-maleic anhydride copolymer, styrenic copolymer, functionalizedstyrenic copolymer, functionalized styrenic terpolymer, styrenicterpolymer, cellulose polymer, liquid crystal polymer, ethylene-vinylacetate copolymers, polyurea, and polysiloxane or anymetallocene-catalyzed polymers of these species.

Suitable polyamides for use as an additional polymeric material incompositions within the scope of the present invention also includeresins obtained by: (1) polycondensation of (a) a dicarboxylic acid,such as oxalic acid, adipic acid, sebacic acid, terephthalic acid,isophthalic acid, or 1,4-cyclohexanedicarboxylic acid, with (b) adiamine, such as ethylenediamine, tetramethylenediamine,pentamethylenediamine, hexamethylenediamine, or decamethylenediamine,1,4-cyclohexanediamine, or m-xylylenediamine; (2) a ring-openingpolymerization of cyclic lactam, such as ε-caprolactam or Ω-laurolactam;(3) polycondensation of an aminocarboxylic acid, such as 6-aminocaproicacid, 9-aminononanoic acid, 11-aminoundecanoic acid, or12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam witha dicarboxylic acid and a diamine. Specific examples of suitablepolyamides include NYLON 6, NYLON 66, NYLON 610, NYLON 11, NYLON 12,copolymerized NYLON, NYLON MXD6, and NYLON 46.

Suitable peroxide initiating agents include dicumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy) hexane;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne;2,5-dimethyl-2,5-di(benzoylperoxy)hexane;2,2′-bis(t-butylperoxy)-di-iso-propylbenzene;1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane; n-butyl4,4-bis(t-butyl-peroxy)valerate; t-butyl perbenzoate; benzoyl peroxide;n-butyl 4,4′-bis(butylperoxy) valerate; di-t-butyl peroxide; or2,5-di-(t-butylperoxy)-2,5-dimethyl hexane, lauryl peroxide, t-butylhydroperoxide, α-α bis(t-butylperoxy)diisopropylbenzene,di(2-t-butyl-peroxyisopropyl)benzene, di-t-amyl peroxide, di-t-butylperoxide. Preferably, the rubber composition includes from about 0.25 toabout 5.0 parts by weight peroxide per 100 parts by weight rubber (phr),more preferably 0.5 phr to 3 phr, most preferably 0.5 phr to 1.5 phr. Ina most preferred embodiment, the peroxide is present in an amount ofabout 0.8 phr. These ranges of peroxide are given assuming the peroxideis 100% active, without accounting for any carrier that might bepresent. Because many commercially available peroxides are sold alongwith a carrier compound, the actual amount of active peroxide presentmust be calculated. Commercially-available peroxide initiating agentsinclude DICUP™ family of dicumyl peroxides (including DICUP® R, DICUP®40C and DICUP® 40KE) available from Crompton (Geo Specialty Chemicals).Similar initiating agents are available from AkroChem, Lanxess,Flexsys/Harwick and R.T. Vanderbilt. Another commercially-available andpreferred initiating agent is TRIGONOX® 265-50B from Akzo Nobel, whichis a mixture of 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane anddi(2-t-butylperoxyisopropyl) benzene. TRIGONOX® peroxides are generallysold on a carrier compound.

Suitable reactive co-agents include, but are not limited to, metal saltsof acrylic acid or methacrylic acid wherein the metal is zinc,magnesium, calcium, barium, tin, aluminum, lithium, sodium, potassium,iron, zirconium, and bismuth. Zinc diacrylate (ZDA) is preferred, butthe present invention is not limited thereto. ZDA provides golf ballswith a high initial velocity. The ZDA can be of various grades ofpurity. For the purposes of this invention, the lower the quantity ofzinc stearate present in the ZDA the higher the ZDA purity. ZDAcontaining less than about 10% zinc stearate is preferable. Morepreferable is ZDA containing about 4-8% zinc stearate. Suitable,commercially available zinc diacrylates include those from Sartomer Co.The preferred concentrations of ZDA that can be used are about 10 phr toabout 55 phr, preferably 10 phr to about 40 phr, alternatively about 15phr to about 40 phr, more preferably 20 phr to about 35 phr, mostpreferably 25 phr to about 35 phr. In a particularly preferredembodiment, the reactive co-agent is present in an amount of about 21phr to 31 phr, preferably about 29 phr to about 31 phr.

Additional preferred co-agents that may be used alone or in combinationwith those mentioned above include, but are not limited to,trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, andthe like. It is understood by those skilled in the art, that in the casewhere these co-agents may be liquids at room temperature, it may beadvantageous to disperse these compounds on a suitable carrier topromote ease of incorporation in the rubber mixture.

Antioxidants are compounds that inhibit or prevent the oxidativebreakdown of elastomers, and/or inhibit or prevent reactions that arepromoted by oxygen radicals. Some exemplary antioxidants that may beused in the present invention include, but are not limited to, quinolinetype antioxidants, amine type antioxidants, and phenolic typeantioxidants. A preferred antioxidant is2,2′-methylene-bis-(4-methyl-6-t-butylphenol) available as VANOX® MBPCfrom R.T. Vanderbilt. Other polyphenolic antioxidants include VANOX® T,VANOX® L, VANOX® SKT, VANOX® SWP, VANOX® 13 and VANOX® 1290.

Preferably, about 0.25 phr to about 1.5 phr of peroxide as calculated at100% active can be added to the core formulation, more preferably about0.5 phr to about 1.2 phr, and most preferably about 0.7 phr to about 1.0phr. The ZDA amount can be varied to suit the desired compression, spinand feel of the resulting golf ball. The cure regime can have atemperature range between from about 290° F. to about 335° F., morepreferably about 300° F. to about 325° F., and the stock is held at thattemperature for at least about 10 minutes to about 30 minutes.

To form the steep “positive” hardness gradient across the outer corelayer of the present invention, it is preferred that agradient-promoting additive (GPA) is present. Suitable GPA's include,but are not limited to benzoquinones, resorcinols, catechols,quinhydrones, and hydroquinones. Those, and other methods and materialfor creating a steep “positive” hardness gradient are disclosed in U.S.patent application Ser. Nos. 12/168,979; 12/168,987; 12/168,995; and12/169,002, which are incorporated herein by reference thereto.

The thermoset rubber composition of the present invention may alsoinclude an optional soft and fast agent. As used herein, “soft and fastagent” means any compound or a blend thereof that that is capable ofmaking a core 1) softer (lower compression) at constant COR or 2) have ahigher COR at equal compression, or any combination thereof, whencompared to a core equivalently prepared without a soft and fast agent.Preferably, the composition of the present invention contains from about0.05 phr to about 10.0 phr soft and fast agent. In one embodiment, thesoft and fast agent is present in an amount of about 0.05 phr to about3.0 phr, preferably about 0.05 phr to about 2.0 phr, more preferablyabout 0.05 phr to about 1.0 phr. In another embodiment, the soft andfast agent is present in an amount of about 2.0 phr to about 5.0 phr,preferably about 2.35 phr to about 4.0 phr, and more preferably about2.35 phr to about 3.0 phr. In an alternative high concentrationembodiment, the soft and fast agent is present in an amount of about 5.0phr to about 10.0 phr, more preferably about 6.0 phr to about 9.0 phr,most preferably about 7.0 phr to about 8.0 phr. In a most preferredembodiment, the soft and fast agent is present in an amount of about 2.6phr.

Suitable soft and fast agents include, but are not limited to,organosulfur or metal-containing organosulfur compounds, an organicsulfur compound, including mono, di, and polysulfides, a thiol, ormercapto compound, an inorganic sulfide compound, a Group VIA compound,or mixtures thereof. The soft and fast agent component may also be ablend of an organosulfur compound and an inorganic sulfide compound.

Suitable soft and fast agents of the present invention include, but arenot limited to those having the following general formula:

where R₁-R₅ can be C₁-C₈ alkyl groups; halogen groups; thiol groups(—SH), carboxylated groups; sulfonated groups; and hydrogen; in anyorder; and also pentafluorothiophenol; 2-fluorothiophenol;3-fluorothiophenol; 4-fluorothiophenol; 2,3-fluorothiophenol;2,4-fluorothiophenol; 3,4-fluorothiophenol; 3,5-fluorothiophenol2,3,4-fluorothiophenol; 3,4,5-fluorothiophenol;2,3,4,5-tetrafluorothiophenol; 2,3,5,6-tetrafluorothiophenol;4-chlorotetrafluorothiophenol; pentachlorothiophenol;2-chlorothiophenol; 3-chlorothiophenol; 4-chlorothiophenol;2,3-chlorothiophenol; 2,4-chlorothiophenol; 3,4-chlorothiophenol;3,5-chlorothiophenol; 2,3,4-chlorothiophenol; 3,4,5-chlorothiophenol;2,3,4,5-tetrachlorothiophenol; 2,3,5,6-tetrachlorothiophenol;pentabromothiophenol; 2-bromothiophenol; 3-bromothiophenol;4-bromothiophenol; 2,3-bromothiophenol; 2,4-bromothiophenol;3,4-bromothiophenol; 3,5-bromothiophenol; 2,3,4-bromothiophenol;3,4,5-bromothiophenol; 2,3,4,5-tetrabromothiophenol;2,3,5,6-tetrabromothiophenol; pentaiodothiophenol; 2-iodothiophenol;3-iodothiophenol; 4-iodothiophenol; 2,3-iodothiophenol;2,4-iodothiophenol; 3,4-iodothiophenol; 3,5-iodothiophenol;2,3,4-iodothiophenol; 3,4,5-iodothiophenol; 2,3,4,5-tetraiodothiophenol;2,3,5,6-tetraiodothiophenoland; and their zinc salts. Preferably, thehalogenated thiophenol compound is pentachlorothiophenol, which iscommercially available in neat form or under the tradename STRUKTOL®, aclay-based carrier containing the sulfur compound pentachlorothiophenolloaded at 45 percent (correlating to 2.4 parts PCTP). STRUKTOL® iscommercially available from Struktol Company of America of Stow, Ohio.PCTP is commercially available in neat form from eChinachem of SanFrancisco, Calif. and in the salt form, also from eChinachem. Mostpreferably, the halogenated thiophenol compound is the zinc salt ofpentachlorothiophenol, which is commercially available from eChinachem.

As used herein when referring to the invention, the term “organosulfurcompound(s)” refers to any compound containing carbon, hydrogen, andsulfur, where the sulfur is directly bonded to at least 1 carbon. Asused herein, the term “sulfur compound” means a compound that iselemental sulfur, polymeric sulfur, or a combination thereof. It shouldbe further understood that the term “elemental sulfur” refers to thering structure of S₈ and that “polymeric sulfur” is a structureincluding at least one additional sulfur relative to elemental sulfur.

Additional suitable examples of soft and fast agents (that are alsobelieved to be cis-to-trans catalysts) include, but are not limited to,4,4′-diphenyl disulfide; 4,4′-ditolyl disulfide; 2,2′-benzamido diphenyldisulfide; bis(2-aminophenyl)disulfide; bis(4-aminophenyl)disulfide;bis(3-aminophenyl)disulfide; 2,2′-bis(4-aminonaphthyl)disulfide;2,2′-bis(3-aminonaphthyl)disulfide; 2,2′-bis(4-aminonaphthyl)disulfide;2,2′-bis(5-aminonaphthyl)disulfide; 2,2′-bis(6-aminonaphthyl)disulfide;2,2′-bis(7-aminonaphthyl)disulfide; 2,2′-bis(8-aminonaphthyl)disulfide;1,1′-bis(2-aminonaphthyl)disulfide; 1,1′-bis(3-aminonaphthyl)disulfide;1,1′-bis(3-aminonaphthyl)disulfide; 1,1′-bis(4-aminonaphthyl)disulfide;1,1′-bis(5-aminonaphthyl)disulfide; 1,1′-bis(6-aminonaphthyl)disulfide;1,1′-bis(7-aminonaphthyl)disulfide; 1,1′-bis(8-aminonaphthyl)disulfide;1,2′-diamino-1,2′-dithiodinaphthalene;2,3′-diamino-1,2′-dithiodinaphthalene; bis(4-chlorophenyl)disulfide;bis(2-chlorophenyl)disulfide; bis(3-chlorophenyl)disulfide;bis(4-bromophenyl)disulfide; bis(2-bromophenyl)disulfide;bis(3-bromophenyl)disulfide; bis(4-fluorophenyl)disulfide;bis(4-iodophenyl)disulfide; bis(2,5-dichlorophenyl)disulfide;bis(3,5-dichlorophenyl)disulfide; bis(2,4-dichlorophenyl)disulfide;bis(2,6-dichlorophenyl)disulfide; bis(2,5-dibromophenyl)disulfide;bis(3,5-dibromophenyl)disulfide; bis(2-chloro-5-bromophenyl)disulfide;bis(2,4,6-trichlorophenyl)disulfide;bis(2,3,4,5,6-pentachlorophenyl)disulfide; bis(4-cyanophenyl)disulfide;bis(2-cyanophenyl)disulfide; bis(4-nitrophenyl)disulfide;bis(2-nitrophenyl)disulfide; 2,2′-dithiobenzoic acid ethylester;2,2′-dithiobenzoic acid methylester; 2,2′-dithiobenzoic acid;4,4′-dithiobenzoic acid ethylester; bis(4-acetylphenyl)disulfide;bis(2-acetylphenyl)disulfide; bis(4-formylphenyl)disulfide;bis(4-carbamoylphenyl)disulfide; 1,1′-dinaphthyl disulfide;2,2′-dinaphthyl disulfide; 1,2′-dinaphthyl disulfide;2,2′-bis(1-chlorodinaphthyl)disulfide;2,2′-bis(1-bromonaphthyl)disulfide; 1,1′-bis(2-chloronaphthyl)disulfide;2,2′-bis(1-cyanonaphthyl)disulfide; 2,2′-bis(1-acetylnaphthyl)disulfide;and the like; or a mixture thereof. Preferred organosulfur componentsinclude 4,4′-diphenyl disulfide, 4,4′-ditolyl disulfide, or2,2′-benzamido diphenyl disulfide, or a mixture thereof. A morepreferred organosulfur component includes 4,4′-ditolyl disulfide. Inanother embodiment, metal-containing organosulfur components can be usedaccording to the invention. Suitable metal-containing organosulfurcomponents include, but are not limited to, cadmium, copper, lead, andtellurium analogs of diethyldithiocarbamate, diamyldithiocarbamate, anddimethyldithiocarbamate, or mixtures thereof.

Suitable substituted or unsubstituted aromatic organic components thatdo not include sulfur or a metal include, but are not limited to,4,4′-diphenyl acetylene, azobenzene, or a mixture thereof. The aromaticorganic group preferably ranges in size from C₆ to C₂₀, and morepreferably from C₆ to C₁₀. Suitable inorganic sulfide componentsinclude, but are not limited to titanium sulfide, manganese sulfide, andsulfide analogs of iron, calcium, cobalt, molybdenum, tungsten, copper,selenium, yttrium, zinc, tin, and bismuth.

A substituted or unsubstituted aromatic organic compound is alsosuitable as a soft and fast agent. Suitable substituted or unsubstitutedaromatic organic components include, but are not limited to, componentshaving the formula (R₁)_(x)—R₃-M-R₄—(R₂)_(y), wherein R₁ and R₂ are eachhydrogen or a substituted or unsubstituted C₁₋₂₀ linear, branched, orcyclic alkyl, alkoxy, or alkylthio group, or a single, multiple, orfused ring C₆ to C₂₄ aromatic group; x and y are each an integer from 0to 5; R₃ and R₄ are each selected from a single, multiple, or fused ringC₆ to C₂₄ aromatic group; and M includes an azo group or a metalcomponent. R₃ and R₄ are each preferably selected from a C₆ to C₁₀aromatic group, more preferably selected from phenyl, benzyl, naphthyl,benzamido, and benzothiazyl. R₁ and R₂ are each preferably selected froma substituted or unsubstituted C₁ to C₁₀ linear, branched, or cyclicalkyl, alkoxy, or alkylthio group or a C₆ to C₁₀ aromatic group. WhenR₁, R₂, R₃, or R₄, are substituted, the substitution may include one ormore of the following substituent groups: hydroxy and metal saltsthereof; mercapto and metal salts thereof; halogen; amino, nitro, cyano,and amido; carboxyl including esters, acids, and metal salts thereof;silyl; acrylates and metal salts thereof; sulfonyl or sulfonamide; andphosphates and phosphites. When M is a metal component, it may be anysuitable elemental metal available to those of ordinary skill in theart. Typically, the metal will be a transition metal, althoughpreferably it is tellurium or selenium. In one embodiment, the aromaticorganic compound is substantially free of metal, while in anotherembodiment the aromatic organic compound is completely free of metal.

The soft and fast agent can also include a Group VIA component.Elemental sulfur and polymeric sulfur are commercially available fromElastochem, Inc. of Chardon, Ohio Exemplary sulfur catalyst compoundsinclude PB(RM-S)-80 elemental sulfur and PB(CRST)-65 polymeric sulfur,each of which is available from Elastochem, Inc. An exemplary telluriumcatalyst under the tradename TELLOY® and an exemplary selenium catalystunder the tradename VANDEX® are each commercially available from RTVanderbilt.

Other suitable soft and fast agents include, but are not limited to,hydroquinones, benzoquinones, quinhydrones, catechols, and resorcinols.Suitable compounds include, but are not limited to, those disclosed inU.S. patent application Ser. No. 11/829,461, the disclosure of which isincorporated herein in its entirety by reference thereto.

Fillers may also be added to the thermoset rubber composition of thecore to adjust the density of the composition, up or down. Typically,fillers include materials such as tungsten, zinc oxide, barium sulfate,silica, calcium carbonate, zinc carbonate, metals, metal oxides andsalts, regrind (recycled core material typically ground to about 30 meshparticle), high-Mooney-viscosity rubber regrind, trans-regrind corematerial (recycled core material containing high trans-isomer ofpolybutadiene), and the like. When trans-regrind is present, the amountof trans-isomer is preferably between about 10% and about 60%. In apreferred embodiment of the invention, the core comprises polybutadienehaving a cis-isomer content of greater than about 95% and trans-regrindcore material (already vulcanized) as a filler. Any particle sizetrans-regrind core material is sufficient, but is preferably less thanabout 125 μm.

Fillers added to one or more portions of the golf ball typically includeprocessing aids or compounds to affect rheological and mixingproperties, density-modifying fillers, tear strength, or reinforcementfillers, and the like. The fillers are generally inorganic, and suitablefillers include numerous metals or metal oxides, such as zinc oxide andtin oxide, as well as barium sulfate, zinc sulfate, calcium carbonate,barium carbonate, clay, tungsten, tungsten carbide, an array of silicas,and mixtures thereof. Fillers may also include various foaming agents orblowing agents which may be readily selected by one of ordinary skill inthe art. Fillers may include polymeric, ceramic, metal, and glassmicrospheres may be solid or hollow, and filled or unfilled. Fillers aretypically also added to one or more portions of the golf ball to modifythe density thereof to conform to uniform golf ball standards. Fillersmay also be used to modify the weight of the center or at least oneadditional layer for specialty balls, e.g., a lower weight ball ispreferred for a player having a low swing speed.

Materials such as tungsten, zinc oxide, barium sulfate, silica, calciumcarbonate, zinc carbonate, metals, metal oxides and salts, and regrind(recycled core material typically ground to about 30 mesh particle) arealso suitable fillers.

The polybutadiene and/or any other base rubber or elastomer system mayalso be foamed, or filled with hollow microspheres or with expandablemicrospheres which expand at a set temperature during the curing processto any low specific gravity level. Other ingredients such as sulfuraccelerators, e.g., tetra methylthiuram di, tri, or tetrasulfide, and/ormetal-containing organosulfur components may also be used according tothe invention. Suitable metal-containing organosulfur acceleratorsinclude, but are not limited to, cadmium, copper, lead, and telluriumanalogs of diethyldithiocarbamate, diamyldithiocarbamate, anddimethyldithiocarbamate, or mixtures thereof. Other ingredients such asprocessing aids e.g., fatty acids and/or their metal salts, processingoils, dyes and pigments, as well as other additives known to one skilledin the art may also be used in the present invention in amountssufficient to achieve the purpose for which they are typically used.

There are a number of preferred embodiments defined by the presentinvention, which is preferably a golf ball having a “dual core”including a solid thermoplastic inner core layer having a “negative” or“positive” hardness gradient, preferably “positive” and a rubber-basedouter core layer having a steep “negative” or “positive” hardnessgradient, preferably “positive.”

Referring to FIG. 1, the center (mid-point) of the thermoplastic innercore layer should have a hardness of at least about 90 Shore C,preferably from about 90 Shore C to about 100 Shore C, more preferablyfrom about 92 Shore C to about 98 Shore C, and most preferably fromabout 94 Shore C to about 96 Shore C. The outer surface of the innercore layer has a hardness that is greater than the hardness of thecenter of the inner core layer (to define the “negative” hardnessgradient), at least about 85 Shore C, preferably from about 85 Shore Cto about 95 Shore C, more preferably from about 87 Shore C to about 93Shore C, and most preferably about 89 Shore C to about 91 Shore C.

The inner surface of the thermoset rubber outer core layer has a Shore Chardness of about 50 Shore C to about 60 Shore C, preferably about 52Shore C to about 58 Shore C, more preferably from about 54 Shore C toabout 56 Shore C. The outer surface of the outer core layer has ahardness that is substantially greater than the hardness of the innersurface of the outer core layer (to define the steep “positive” hardnessgradient), at least about 82 Shore C, preferably about 82 Shore C toabout 92 Shore C, more preferably about 84 Shore C to about 90 Shore C,most preferably about 86 Shore C to about 88 Shore C. The gradientshould be steep—at least 25 Shore C, preferably 25 Shore C to 45 ShoreC, more preferably 25 Shore C to 40 Shore C, and most preferably 30Shore C to 35 shore C.

The difference in hardness, Δh, between the outer surface of the innercore layer and the inner surface of the outer core layer, should be atleast 25 Shore C, preferably 25 Shore C to 45 Shore C, more preferably25 Shore C to 40 Shore C, and most preferably 30 Shore C to 35 shore C(meaning that the inner surface of the outer core layer is substantiallysofter than the outer surface of the inner core). In one embodiment, theouter surface of the outer core layer is also softer than the outersurface of the inner core layer, preferably by 1 Shore C to 5 Shore C,more preferably by 1 Shore C to 3 Shore C, and alternatively by 3 ShoreC to 5 Shore C.

The sloped lines in FIG. 1 depict the “direction” of the gradient andare by no means dispositive of the nature of the hardness values betweenthe outer and inner surfaces—while one embodiment certainly is alinearly-sloped hardness gradient for both core layers having the valuesdepicted in the Figure, it should be understood that the interimhardness values are not necessarily linearly related (i.e., they can bedispersed above and/or below the line).

There are a number of alternative embodiments defined by the presentinvention, which is preferably a golf ball including a single, solidthermoplastic core having a “positive” or “negative” hardness gradient,or a “dual core,” in which at least one, preferably both, of the innercore and outer core layer are formed from a thermoplastic material andhave a “positive” or “negative” hardness gradient. In one preferredembodiment, a “low spin” embodiment, the inner surface of the outer corelayer is harder than the outer surface of the inner core. In a secondpreferred embodiment, a “high spin” embodiment, the inner surface of theouter core layer is softer than the outer surface of the inner core. Thealternative to these embodiments, to form a “positive” hardnessgradient, are also preferred.

“Positive” hardness gradient embodiments, single solid core: the surfacehardness of the core can range from 25 Shore D to 90 Shore D, preferably45 Shore D to 70 Shore D. The surface hardness is most preferably 68Shore D, 60 Shore D, or 49 Shore D. The corresponding hardness of thecenter of the solid core may range from 30 Shore D to 80 Shore D, morepreferably 40 Shore D to 65 Shore D, and most preferably 61 Shore D, 52Shore D, or 43 Shore D, respectively. The “positive” gradient ispreferably 7, 8, or 6, respectively. Corresponding Atti compressionvalues may be 135, 110, or 90, respectively. The COR of these cores mayrange from 0.800 to 0.850, preferably 0.803 to 0.848.

“Positive” hardness gradient embodiments, dual core: the outer coresurface hardness may range from 25 Shore D to 90 Shore D, morepreferably 45 Shore D to 70 Shore D, and most preferably 68 Shore D, 61Shore D, or 49 Shore D. The inner surface of the outer core may have acorresponding hardness of 61 Shore D, 61 Shore D, or 43 Shore D,respectively. The surface of the inner core can range from 40 Shore D to65 Shore D, but is preferably and correspondingly 43 Shore D, 60 ShoreD, or 49 Shore D, respectively. The center hardness of the inner corecan range from 30 Shore D to 80 Shore D, more preferably 40 Shore D to55 Shore D, and most preferably 43 Shore D, 50 Shore D, or 43 Shore D,respectively. The “positive” gradient is preferably 25, 11, or 6,respectively. The corresponding compressions are 100, 97, or 92 and CORvalues are 0.799, 0.832, or 0.801, respectively.

“Negative” hardness gradient embodiments, single solid core: the surfacehardness of the core can range from 20 Shore D to 80 Shore D, morepreferably 35 Shore D to 60 Shore D. The surface hardness is mostpreferably 56 Shore D, 45 Shore D, or 40 Shore D. The correspondingcenter hardness may range from 30 Shore D to 75 Shore D, preferably 40Shore D to 65 Shore D, and more preferably 61 Shore D, 52 Shore D, or 43Shore D, respectively. The “negative” gradient is preferably −5, −7, or−3, respectively. Corresponding Atti compression values may be 111, 104,or 85, respectively. The COR of these cores may range from 0.790 to0.820, preferably 0.795 to 0.812.

“Negative” hardness gradient embodiments, dual core: the outer coresurface hardness may range from 20 Shore D to 80 Shore D, preferably 35Shore D to 55 Shore D, more preferably 45 Shore D, 40 Shore D, or 52Shore D. The inner surface of the outer core may have a correspondinghardness of 52 Shore D, 43 Shore D, or 52 Shore D, respectively. Thesurface of the inner core can range from 30 Shore D to 75 Shore D,preferably 50 Shore D to 65 Shore D, more preferably and correspondingly61 Shore D, 52 Shore D, or 56 Shore D, respectively. The center hardnessof the inner core can range from 50 Shore D to 65 Shore D, but ispreferably 61 Shore D, 52 Shore D, or 61 Shore D, respectively. The“negative” gradient is steep, preferably −16, −12, or −9, respectively.The corresponding compressions are 117, 92, or 115 and COR values are0.799, 0.832, or 0.801, respectively.

In a “low spin” embodiment of the present invention, the hardness of thethermoplastic inner core (at any point—surface, center, or otherwise)ranges from 30 Shore C to 80 Shore C, more preferably 40 Shore C to 75Shore C, most preferably 45 Shore C to 70 Shore C. Concurrently, thehardness of the outer core layer (at any point—surface, inner surface,or otherwise) ranges from 60 Shore C to 95 Shore C, more preferably 60Shore C to 90 Shore C, most preferably 65 Shore C to 80 Shore C.

In a “high spin” embodiment, the hardness of the thermoplastic innercore ranges from 60 Shore C to 95 Shore C, more preferably 60 Shore C to90 Shore C, most preferably 65 Shore C to 80 Shore C. Concurrently, thehardness of the outer core layer ranges from 30 Shore C to 80 Shore C,more preferably 40 Shore C to 75 Shore C, most preferably 45 Shore C to70 Shore C.

In the embodiment where the interface (i.e., the area where the twocomponents meet) of the outer core layer and the inner core hassubstantially the same hardness, the ranges provided for either the “lowspin” or “high spin” embodiments are sufficient, as long as the“negative” hardness gradient is maintained and the hardness value at theinner surface of the outer core layer is roughly the same as thehardness value at the outer surface of the inner core.

The surface hardness of a core is obtained from the average of a numberof measurements taken from opposing hemispheres of a core, taking careto avoid making measurements on the parting line of the core or onsurface defects, such as holes or protrusions. Hardness measurements aremade pursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plasticby Means of a Durometer.” Because of the curved surface of a core, caremust be taken to insure that the core is centered under the durometerindentor before a surface hardness reading is obtained. A calibrated,digital durometer, capable of reading to 0.1 hardness units is used forall hardness measurements and is set to take hardness readings at 1second after the maximum reading is obtained. The digital durometer mustbe attached to, and its foot made parallel to, the base of an automaticstand, such that the weight on the durometer and attack rate conform toASTM D-2240.

To prepare a core for hardness gradient measurements, the core is gentlypressed into a hemispherical holder having an internal diameterapproximately slightly smaller than the diameter of the core, such thatthe core is held in place in the hemispherical portion of the holderwhile concurrently leaving the geometric central plane of the coreexposed. The core is secured in the holder by friction, such that itwill not move during the cutting and grinding steps, but the friction isnot so excessive that distortion of the natural shape of the core wouldresult. The core is secured such that the parting line of the core isroughly parallel to the top of the holder. The diameter of the core ismeasured 90 degrees to this orientation prior to securing. A measurementis also made from the bottom of the holder to the top of the core toprovide a reference point for future calculations. A rough cut, madeslightly above the exposed geometric center of the core using a band sawor other appropriate cutting tool, making sure that the core does notmove in the holder during this step. The remainder of the core, still inthe holder, is secured to the base plate of a surface grinding machine.The exposed ‘rough’ core surface is ground to a smooth, flat surface,revealing the geometric center of the core, which can be verified bymeasuring the height of the bottom of the holder to the exposed surfaceof the core, making sure that exactly half of the original height of thecore, as measured above, has been removed to within ±0.004 inches.

Leaving the core in the holder, the center of the core is found with acenter square and carefully marked and the hardness is measured at thecenter mark. Hardness measurements at any distance from the center ofthe core may be measured by drawing a line radially outward from thecenter mark, and measuring and marking the distance from the center,typically in 2-mm increments. All hardness measurements performed on theplane passing through the geometric center are performed while the coreis still in the holder and without having disturbed its orientation,such that the test surface is constantly parallel to the bottom of theholder. The hardness difference from any predetermined location on thecore is calculated as the average surface hardness minus the hardness atthe appropriate reference point, e.g., at the center of the core forsingle, solid core, such that a core surface softer than its center willhave a negative hardness gradient.

In all preferred embodiments of invention, the hardness of the core atthe surface is always less than or greater than (i.e., different) thanthe hardness of the core at the center.

Furthermore, the center hardness of the core is not necessarily thehardest point in the core. Additionally, the lowest hardness anywhere inthe core does not have to occur at the surface. In some embodiments, thelowest hardness value occurs within about the outer 6 mm of the coresurface. However, the lowest hardness value within the core can occur atany point from the surface, up to, but not including the center, as longas the surface hardness is still different from the hardness of thecenter.

As described above, the preferred embodiment is a golf ball having adual core. The dual core includes an inner core formed from athermoplastic material and the outer core layer is formed from athermoset material. The inner core material exhibits a ‘shallow’“positive hardness gradient” across its radius. The outer core layermaterial exhibits a ‘steep’ “positive hardness gradient across itsthickness, the slope of the gradient being greater than that of thegradient of the inner core. Hardness measurements are made as describedherein. The hardness measurements for the gradient of the inner core aretaken across the radius of a cross-section of the inner core. Thehardness measurements for the gradient of the outer core layer are takenacross the thickness of a cross-section of the outer core layer.

In one embodiment, the thermoplastic inner core has an outer diameter ofabout 0.5 inches. The hardness gradient is preferably less than about 5Shore C, more preferably about 1 to 5 Shore C, and most preferably about2 to 4 Shore C. The outer core layer is about 0.515 inches thick and hasa hardness gradient that is about 6 Shore C or greater, more preferablyabout 6 to 20 Shore C, and most preferably about 10 to 18 Shore C.Alternatively, the hardness gradient of the inner core is preferablyless than about 4 Shore D, more preferably about 1 to 4 Shore D, andmost preferably about 2 to 4 Shore D and the hardness gradient of theouter core layer is about 5 Shore D or greater, more preferably about 5to 20 Shore D, and most preferably about 10 to 18 Shore D.

In a second embodiment, the thermoplastic inner core has an outerdiameter of about 1.0 inch. The hardness gradient is preferably lessthan about 10 Shore C, more preferably about 1 to 10 Shore C, and mostpreferably about 2 to 7 Shore C. The outer core layer has a thickness ofabout 0.275 inches and has a hardness gradient that is about 11 Shore Cor greater, more preferably about 11 to 20 Shore C, and most preferablyabout 11 to 15 Shore C. Alternatively, the hardness gradient of theinner core is preferably less than about 10 Shore D, more preferablyabout 1 to 8 Shore D, and most preferably about 2 to 6 Shore D and thehardness gradient of the outer core layer is about 11 Shore D orgreater, more preferably about 11 to 20 Shore D, and most preferablyabout 11 to 15 Shore D.

In another embodiment of the present invention, the thermoplastic innercore has an outer diameter of about 1.13 inches. The hardness gradientacross the radius of the inner core is preferably less than about 11Shore C, more preferably about 1 to 11 Shore C, and most preferablyabout 3 to 8 Shore C. The outer core layer preferably has a thickness ofabout 0.225 inches and has a hardness gradient that is about 12 Shore Cor greater, more preferably about 12 to 20 Shore C, and most preferablyabout 12 to 16 Shore C. Alternatively, the hardness gradient of theinner core is preferably less than about 11 Shore D, more preferablyabout 1 to 9 Shore D, and most preferably about 2 to 7 Shore D and thehardness gradient of the outer core layer is about 12 Shore D orgreater, more preferably about 12 to 20 Shore D, and most preferablyabout 14 to 18 Shore D.

Representative cores of the present invention are depicted in FIGS. 2-4.FIG. 2 shows the hardness gradient (in Shore C and D) for a golf ballcore having an inner core having a diameter of about 0.5 inches and anouter core layer having a thickness of about 0.515 inches; FIG. 3 showsthe hardness gradient (in Shore C and D) for a golf ball core having aninner core having a diameter of about 1.0 inch and an outer core layerhaving a thickness of about 0.275 inches; and FIG. 4 shows the hardnessgradient (in Shore C and D) for a golf ball core having an inner corehaving a diameter of about 1.13 inches and an outer core layer having athickness of about 0.225 inches. It should be noted that the hardnessgradients are not required to be linear and that points between theouter- and inner-most hardness measurements may very well be higher orlower than those gradient-defining hardness measurements.

The inventive core layers each have a slope defined by the hardnessgradient across the cross-section of either the inner core or the outercore layer. A ratio of the slope of the hardness gradient of the outercore layer to the inner core is preferably greater than 1, morepreferably greater than about 1.2 or 1.3, most preferably greater thanabout 1.4 or 1.5. In one preferred embodiment, the ratio of the slope ofthe hardness gradient of the outer core layer to the inner core isgreater than about 2.

The above embodiments may be tailored to meet predetermined performanceproperties. For example, alternative embodiments include those having aninner core having an outer diameter of about 0.250 inches to about 1.550inches, preferably about 0.500 inches to about 1.500 inches, and morepreferably about 0.750 inches to about 1.400 inches. In preferredembodiments, the inner core has an outer diameter of about 1.000 inch,1.200 inches, or 1.300 inches, with a most preferred outer diameterbeing 1.130 inches. The outer core layer should have an outer diameter(the entire dual core) of about 1.30 inches to about 1.620 inches,preferably 1.400 inches to about 1.600 inches, and more preferably about1.500 inches to about 1.590 inches. In preferred embodiments, the outercore layer has an outer diameter of about 1.510 inches, 1.530 inches, ormost preferably 1.550 inches.

While layers of the inventive golf ball may be formed from a variety ofdiffering cover materials (both intermediate layer(s) and outer coverlayer) described herein, preferred cover materials include, but are notlimited to:

(1) Polyurethanes, such as those prepared from polyols or polyamines anddiisocyanates or polyisocyanates and/or their prepolymers, and thosedisclosed in U.S. Pat. Nos. 5,334,673 and 6,506,851;

(2) Polyureas, such as those disclosed in U.S. Pat. Nos. 5,484,870 and6,835,794; and

(3) Polyurethane-urea hybrids, blends or copolymers comprising urethaneor urea segments.

Suitable polyurethane compositions comprise a reaction product of atleast one polyisocyanate and at least one curing agent. The curing agentcan include, for example, one or more polyamines, one or more polyols,or a combination thereof. The polyisocyanate can be combined with one ormore polyols to form a prepolymer, which is then combined with the atleast one curing agent. Thus, the polyols described herein are suitablefor use in one or both components of the polyurethane material, i.e., aspart of a prepolymer and in the curing agent.

Suitable polyurethanes and polyureas, saturated or unsaturated, andtheir components, such as prepolymers, isocyanates, polyols, polyamines,curatives, etc. are disclosed in U.S. patent application Ser. No.11/772,903, which is incorporated herein by reference thereto.

Alternatively, other suitable polymers for use in cover layers includepartially- or fully-neutralized ionomers, metallocene or othersingle-site catalyzed polymers, polyesters, polyamides, non-ionomericthermoplastic elastomers, copolyether-esters, copolyether-amides,polycarbonates, polybutadienes, polyisoprenes, polystryrene blockcopolymers (such as styrene-butadiene-styrene),styrene-ethylene-propylene-styrene, styrene-ethylene-butylene-styrene,and blends thereof. Thermosetting polyurethanes or polyureas aresuitable for the outer cover layers of the golf balls of the presentinvention.

In a preferred embodiment, the inventive core is preferably enclosedwith two cover layers, where the inner cover layer has a thickness ofabout 0.01 inches to about 0.06 inches, more preferably about 0.015inches to about 0.040 inches, and most preferably about 0.02 inches toabout 0.035 inches, and the inner cover layer is formed from apartially- or fully-neutralized ionomer having a Shore D hardness ofgreater than about 55, more preferably greater than about 60, and mostpreferably greater than about 65. The outer cover layer should have athickness of about 0.015 inches to about 0.055 inches, more preferablyabout 0.02 inches to about 0.04 inches, and most preferably about 0.025inches to about 0.035 inches, and has a hardness of about Shore D 60 orless, more preferably 55 or less, and most preferably about 52 or less.The inner cover layer is preferably harder than the outer cover layer.The outer cover layer may be formed of a partially- or fully-neutralizediononomer, a polyurethane, polyurea, or blend thereof. A most preferredouter cover layer is a castable or reaction injection moldedpolyurethane, polyurea or copolymer or hybrid thereof having a Shore Dhardness of about 40 to about 50. A most preferred inner cover layermaterial is a partially-neutralized ionomer comprising a zinc, sodium orlithium neutralized ionomer such as SURLYN® 8940, 8945, 9910, 7930,7940, or blend thereof having a Shore D hardness of about 63 to about68.

In another preferred embodiment, the core having a negative hardnessgradient is enclosed with a single layer of cover material having aShore D hardness of from about 20 to about 80, more preferably about 40to about 75 and most preferably about 45 to about 70, and comprises athermoplastic or thermosetting polyurethane, polyurea, polyamide,polyester, polyester elastomer, polyether-amide or polyester-amide,partially or fully neutralized ionomer, polyolefin such as polyethylene,polypropylene, polyethylene copolymers such as ethylene-butyl acrylateor ethylene-methyl acrylate, poly(ethylene methacrylic acid) co-andterpolymers, metallocene-catalyzed polyolefins and polar-groupfunctionalized polyolefins and blends thereof.

One suitable cover material is an ionomer (either conventional or HNP)having a hardness of about 50 to about 70 Shore D. Another preferredcover material is a thermoplastic or thermosetting polyurethane orpolyurea. A preferred ionomer is a high acid ionomer comprising acopolymer of ethylene and methacrylic or acrylic acid and having an acidcontent of at least 16 to about 25 weight percent. In this case thereduced spin contributed by the relatively rigid high acid ionomer maybe offset to some extent by the spin-increasing negative gradient core.The core may have a diameter of about 1.0 inch to about 1.64 inches,preferably about 1.30 inches to about 1.620, and more preferably about1.40 inches to about 1.60 inches.

Another preferred cover material comprises a castable or reactioninjection moldable polyurethane, polyurea, or copolymer or hybrid ofpolyurethane/polyurea. Preferably, this cover is thermosetting but maybe a thermoplastic, having a Shore D hardness of about 20 to about 70,more preferably about 30 to about 65 and most preferably about 35 toabout 60. A moisture vapor barrier layer, such as disclosed in U.S. Pat.Nos. 6,632,147; 6,932,720; 7,004,854; and 7,182,702, all of which areincorporated by reference herein in their entirety, are optionallyemployed between the cover layer and the core.

While any of the embodiments herein may have any known dimple number andpattern, a preferred number of dimples is 252 to 456, and morepreferably is 330 to 392. The dimples may comprise any width, depth, andedge angle disclosed in the prior art and the patterns may comprisesmultitudes of dimples having different widths, depths and edge angles.The parting line configuration of said pattern may be either a straightline or a staggered wave parting line (SWPL). Most preferably the dimplenumber is 330, 332, or 392 and comprises 5 to 7 dimples sizes and theparting line is a SWPL.

Other than in the operating examples, or unless otherwise expresslyspecified, all of the numerical ranges, amounts, values and percentagessuch as those for amounts of materials and others in the specificationmay be read as if prefaced by the word “about” even though the term“about” may not expressly appear with the value, amount or range.Accordingly, unless indicated to the contrary, the numerical parametersset forth in the specification and attached claims are approximationsthat may vary depending upon the desired properties sought to beobtained by the present invention. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical parameter should at least beconstrued in light of the number of reported significant digits and byapplying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Furthermore, when numerical ranges ofvarying scope are set forth herein, it is contemplated that anycombination of these values inclusive of the recited values may be used.

While it is apparent that the illustrative embodiments of the inventiondisclosed herein fulfill the objective stated above, it is appreciatedthat numerous modifications and other embodiments may be devised bythose skilled in the art. Therefore, it will be understood that theappended claims are intended to cover all such modifications andembodiments, which would come within the spirit and scope of the presentinvention.

What is claimed is:
 1. A golf ball comprising: an inner core layercomprising a thermoplastic highly-neutralized ionomer comprising acopolymer of ethylene and an α,β-unsaturated carboxylic acid, an organicacid or salt thereof, and sufficient cation source to neutralize theacid groups of the copolymer by 80% or greater, and having a geometriccenter hardness and a surface hardness to define a first hardnessgradient; an outer core layer disposed about the inner core, the outercore being formed from a homogenous thermoset composition and having aninterior hardness and an outer surface hardness to define a secondhardness gradient; an inner cover layer disposed about outer core layer;and an outer cover layer disposed about the inner cover layer, wherein aslope of the second hardness gradient is greater than a slope of thefirst hardness gradient.
 2. The golf ball of claim 1, wherein a ratio ofthe slope of the second hardness gradient to the slope of the firsthardness gradient is greater than
 1. 3. The golf ball of claim 2,wherein a ratio of the slope of the second hardness gradient to theslope of the first hardness gradient is greater than 1.5.
 4. The golfball of claim 3, wherein a ratio of the slope of the second hardnessgradient to the slope of the first hardness gradient is greater than 2.5. The golf ball of claim 1, wherein the inner core layer has an outerdiameter of about 0.5 inches to about 1.13 inches.
 6. The golf ball ofclaim 1, wherein the acid groups of the copolymer are neutralized by 90%or greater.
 7. The golf ball of claim 6 wherein the acid groups of thecopolymer are neutralized by about 100%.
 8. The golf ball of claim 1,wherein the organic acid or salt thereof comprises barium, lithium,sodium, zinc, bismuth, chromium, cobalt, copper, potassium, strontium,titanium, tungsten, magnesium, cesium, iron, nickel, silver, aluminum,tin, or calcium salts, or salts of fatty acids.
 9. The golf ball ofclaim 8, wherein the fatty acid salt comprises stearic acid, behenicacid, erucic acid, oleic acid, linoelic acid or dimerized derivativesthereof.
 10. The golf ball of claim 8, wherein the organic acid or saltthereof comprises a magnesium salt of oleic acid.
 11. The golf ball ofclaim 1, wherein the outer core layer comprises a soft and fast agent.12. The golf ball of claim 11, wherein the soft and fast agent comprisesa halogenated thiophenol.